Telephones are a crucial part of modern living while at home, but taking them on the road when travelling can get expensive. Mobile providers usually charge inflated "roaming" fees when serving phones carried abroad. Hotels often overcharge for trunk calls from room telephones.

By contrast, a high-speed Internet connection can be used to make voice-over-IP (VoIP) calls to landlines in most industrialised nations for a penny or two a minute; calls to other Internet telephony users on the same service are often free.

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See also: Mobile phones, Computers

Where you have full access to the Internet at a reasonable speed and price, making phone calls over the Internet is the cheapest option. See Internet access for more detail on finding a connection, ideally a free one (video calls using mobile data can get quite expensive).

To make calls, you also need suitable hardware and VoIP software. Your smartphone already has the needed hardware – a 4G phone actually makes VoIP calls – but to avoid the provider's charges, you need independent software. Your computer can be connected to a headset, at least by the USB interface. Many devices include a small built-in camera (webcam), allowing also video calls.

There is a range of VoIP clients; a client is included in most messaging applications, some of which may already be installed on your device. Also video conference and webcam applications may suit your needs. Some of the applications have privacy issues; you may want to read the small print of any end user agreements and choose what companies to trust.

Additionally, for calling phones on the telephony network, you need a provider; they will make the actual call from a gateway near the destination number, and accept calls for you at the gateway. There are a number of such providers ("voice service provider", VSP) and, likewise, many messaging applications include the option of making calls "out" to the telephony network (and possibly to some other VoIP providers). This usually requires explicit registration; test your configuration before departing.

Free calls are possible if both parties have Internet access and are running the same or compatible software. Calls where one party uses a conventional telephone and the other uses an internet connection (such as a Wi-Fi hotspot) are not free, but are far less expensive than conventional overseas telephony. A call to a landline anywhere from London to Los Angeles from the broadband Internet can cost as little as a penny a minute, as the voice service provider (VSP) doesn't have to transport the call to those faraway places – the Internet already does that. The VSP merely finds a least-expensive gateway to convert the call back to landline telephony at destination.

A headset will give better sound quality than the built-in speakers if using a PC or tablet; smaller devices (iPhone, iPod Touch, Blackberry, Android handset) are suited directly for use as telephone handsets, giving the look and feel of mobile telephony with no need for any external hardware. The quality of the actual telephone calls, in any case, will remain at the mercy of the underlying Internet connection. If connection speed is sporadic and unreliable, the audio will contain annoying dropouts; if the connection is consistently fast (both outbound and inbound) an Internet telephone will work well.

Some PC applications suppose you have a good connection and by default use a codec (coder-decoder) which optimizes voice quality at the expense of bandwidth. With a codec optimized for compression, a data rate well under the 56 kbps of a landline connection may suffice; without compression, one voice call plus packet overhead uses about 80kbps and needs this data rate consistently. For some connections you may want to allow much more lag than the default, as delayed packets will otherwise be discarded.

In some destinations, one may rent a computer with Skype from a local Internet store.

Voice

There are various platforms for transmitting voice (and, in some cases, video) over the Internet:

• The Session Initiation Protocol (SIP) is a standard used by many small Internet telephone companies; it's useful as a replacement for conventional telephony. Computer retailers offer hardware which uses this session initiation protocol to connect a standard desk telephone to a virtual Internet phone line; there are also mobile apps (softphones) which let you take this Internet home phone connection with you on your travels. Someone rings your home phone and you seamlessly take the call at a Wi-Fi hotspot half a world away. If your friends have the needed hardware or software (on their computer or smartphone), calls are usually free. The software may support video, file transfer etc. beside voice.
• Nowadays most people use commercial proprietary software (such as Skype or WhatsApp), from which calls between users is free, while calling others incurs fees, if supported at all. These apps may be primarily known for other functions, such as messaging, webcam support or social media features. They may or may not support calls to or from SIP users or the public telephony network, and fees vary.

Fax etc.

A VoIP connection behaves poorly if used as a virtual "telephone line" to operate dial-up modems and fax machines. Internet packets are prone to often be dropped, delayed or delivered out-of-sequence during a call; this might go unnoticed for a voice call, but will cause errors and disconnections that render the connection unusable for fax or data. If you need those, check your options in time before departure.

Blocks and obstacles

VoIP is often insecure Do not assume that calls made this way (or, for that matter, with a phone) are private. Security experts believe that at least the US, China and Russia can tap Skype calls, other VoIP systems are also vulnerable, and there is little reason to suppose that those governments are the only possible eavesdroppers. If you need security against serious attackers, either check the security of your VoIP configuration with the help of a trusted up-to-date security professional, or use some other security evaluated channel instead. Regardless, make sure you prevent breaking into your device, to the best of your abilities.

Some publicly available networks can block VoIP, many are simply too slow, and in some countries, Internet telephony is blocked entirely to protect overpriced national phone monopolies. Public hotspots vary widely in quality; some may provide access to the full Internet, others might provide access to just the Web (which is one Internet application among many) or a limited number of services while blocking everything else. Some may only enable a connection after a user opens a webpage and "agrees" to a long list of incomprehensible conditions and legalese. These issues are independent of the speed of the underlying connection.

VoIP is a good way to maintain contact with friends and family while travelling, who will tolerate the occasional drop-out. It may not be the best way to maintain a connection with important business contacts.

Etisalat, the state-owned telecommunications provider of the United Arab Emirates blocks access to the Skype network entirely. However, Skype is still accessible from some hotels that provide access through 'TheWayOut' Wi-Fi service.

Some providers may block calls placed from IP addresses in various foreign lands, if those foreign countries are a source of fraudulent Internet telephone calls or abnormal patterns of usage. A few providers block calls to certain high-priced destinations, unless they receive a verifiable request from the subscriber to unlock them. The same approach to flagging unusual usage patterns occurs with other on-line services (so repeated attempts to log in from Moscow to a Google account which belongs to a North American user might be flagged as questionable); check with your provider before departure.

A virtual private network (VPN) will allow you to connect to your own home-country office and circumvent many of these issues (you can even appear to still be at your desk when you're actually travelling the world on business), although a few particularly dictatorial nations will deny you access to a VPN.

Equipment and applications

There are various ways to get on-line to make inexpensive voice calls; these fall into two main categories:

• hardware such as self-contained Internet telephones or adapters to plug wireline handsets into the network
• softphones, application software which turns a smartphone, tablet or PC into an Internet telephone

Dedicated devices

Various devices are promoted for home or office use:

• Analogue telephone adapters (which plug into a standard landline handset and a wired Internet connection). Common for residential use, and usually will still work if taken to another city and plugged into the Internet, but with two boxes (a phone and an adapter) too bulky to be easily portable.
• VoIP office telephones, which are self-contained and just need to plug into the Internet. One piece, but still bulky for travellers.
• Various add-ons for laptop or desktop PC's which appear to be wired or wireless telephone handsets, telephone line jacks or headsets. Most are based on using a PC software application (softphone) to do most of the work, while the hardware merely operates as a computer sound card. Just a headset and the integrated sound card would do the job with the right software package.

While certainly capable of providing the functionality of a standard desk telephone, in many cases without the need for a computer, these are intended for fixed installation (such as home or office) as they are awkward to carry.

Smartphone apps

There are various free applications (SipDroid, Vimphone, CSipSimple) which can be used to make telephone calls from Android-based smartphones. As these use the handset's Wi-Fi connection, there is no need for a cellular/mobile telephone subscription. With these apps, a SIP provider is needed to reach standard telephones; costs start at US$0.85/month (per DID number) $US0.009/minute (incoming calls, based on voip.ms).

As with PC's, there are instant messenger applications which can communicate with other Internet users on the same service for free.

As prepaid mobile vendors are flooding the market with under-US$100 Android devices, the costly single-purpose "cordless Wi-Fi Internet phone" handsets are becoming rare. It's actually cheaper to buy the general-purpose Android and install a free app to use it as a cordless VoIP phone.

The form factor of some Android, Blackberry smartphone or iPod devices looks and feels like a telephone handset, making the platforms ideal for running Internet calls over Wi-Fi. No need for a separate microphone and headset, the whole package is one inexpensive pocket-sized device which typically also provides an e-mail client, camera, media player and travel alarm clock.

Capabilities of iPhone/iPod apps are similar to those of Android devices, although specific applications to make SIP calls will vary (Acrobits, Fring, Linphone, Media5-fone, NetDial Sip Phone and Zoiper all exist on both platforms). Apple's proprietary messenger, FaceTime, is supported on all Apple devices.

Laptop and PC

Most of the standard instant messenger and webcam applications (such as Google Voice, Yahoo or Skype) originated on PC's, although some now also have iOS or Android versions. When using a tablet, laptop or PC it may be desirable to add a wired headset or a wireless Bluetooth headset; the audio otherwise will be speakerphone quality at best.

Various SIP-compatible softphones (such as Ekiga) may be used to call from a computer to the telephone network through a SIP provider. Some messenger apps can be used to call telephones for a fee, which is usually higher than the cheapest unbundled SIP voice-over-IP services.

Internet phone companies

Because calls are routed over the Internet, you do not need to use a phone company located where you live or where you travel. There is also no requirement that you obtain a local number from the community in which you live; you can obtain a satellite Internet connection in the wilds of Chicken, Alaska and select a number which claims you're in sunny Arizona. Often, you have to buy a global number separately that allows PSTN phones to call you. Where the number is from makes a difference for people calling you.

SIP Phone companies

There are literally thousands of VOIP companies. It is best to pick a company which has connections either in the country you are calling from or calling to, to avoid unnecessary international hops.

Many (but not all) of these providers will allow free calls over the Internet to other subscribers on the same server, as these internal calls never reach the public switched telephone network (PSTN).

Europe

• Betamax GmbH (VoIP Buster, VoipCheap, VoipDiscount, VoIP Stunt) Germany. Various plans under different branding offer "free calls" to a few dozen countries (in Europe or scattered worldwide, landline) for a few months after purchase of prepaid credits. The Betamax products appear to be limited by IP address, so 'roaming' may not work well. Some brands offer voip in numbers in European countries.
• Localphone VoIP Services UK-based. Free Localphone–Localphone calls, cheap calls over PSTN.
• SipDiscount Luxembourg. Free 1 min trial calls to many countries.

USA

• IConnectHere. New Jersey. Prepaid from $10.00.
• Vitelity, Denver. Unbundled prepaid SIP voice with local North American numbers. Internet fax gateway (send and receive). Fax numbers are US local (various cities) or North American +1-800/888 tollfree.
• Vonage Nominally SIP, but known to lock you out of your device settings – which defeats the point of SIP as an open standard.

Canada

• Les.net. Prepaid SIP, Canada/US inbound (local numbers in most cities), North America tollfree numbers. From $2/month and 1.5 cents/minute, with a Winnipeg (+1-204-666) incoming number included. Can receive FAX (gated to e-mail) but not send FAX.
• VBuzzer, Toronto/York Region. Prepaid SIP, inbound Canada/US numbers, two cents/minute. Fax in/out is possible if using their supplied Windows XP softphone.
• VoIP.ms Montréal. Canada/US local Pay-per-minute( $0.85 USD/month + $0.009 USD/minute) Unlimited plans ($4.25 USD/month + $0.0 USD/minute incoming calls) and toll-free plans ( $1.27 USD/month + $0.027 USD/minute), $15 USD minimum deposit. Multiple points of presence in US, Canada, Australia, France and Netherlands. Fax support with US and Canada DID numbers only.
• MyOwntelco Montréal. Prepaid SIP, North America coverage and access number in more than 3000 cities, local inbound numbers $7/month (most cities), 0.6 cents/minute calls to Canada, US/ Western Europe Landline from 1 cent, Fax to email, International DID, Sip client for smartphone.

Non-SIP phone companies

• Net2Phone
• Skype. Free computer-to-computer calls: pay a fee for Skype-Out service to call anyone else or pay a fee for Skype-In service to get a phone number where people can call your computer. Skype claims to be secure by using strong encryption to protect your messages, but some experts have been scathingly sceptical about those claims. As Skype in some circumstances route calls via third party Skype users, check the bandwidth use.
• United World Telecom

Callback

These websites call you on your homeline and the person you want to call, using normal phones.

• UWT Callback Service.

Direct inward system access

Direct inward system access (DISA) is a feature deployed by some Asterisk PBX-based providers, such as Swiftvox (voip.ms). It functions much like a calling card service; dial your own number using a normal phone, enter a code, then get a dial tone from your voice-over-IP provider's private branch exchange to call back out inexpensively using Internet telephony. It's more expensive than calling with a softphone app from a wi-fi hotspot (as this incurs the cost of both an inbound and an outbound call) but can be a viable alternative to purchasing prepaid calling cards.

A similar concept is a "calling card number" provided by a voice-over-IP carrier as part of the same package (or on the same bill) as Internet telephone service. These can allow travellers to avoid the short expiry dates and many hidden fees on prepaid cards in local convenience stores, but be sure to check that you (or your carrier) have a local access number in the places you plan to visit.

Messenger applications

Yahoo Messenger (YM) allows users of selected countries to call any phone after topping-up (via credit card) starting at $10.00. As with Skype-to-Skype calls, YM calls to another active YM user on the Internet are free of charge.

Google Voice may be used to make inexpensive calls and can provide a local number in the United States of America.

Apple's FaceTime allows free video calls between users of any Apple devices. Unlike Skype's video calling, FaceTime is not available for non-Apple devices (such as Androids or Windows/Linux PC's).

Other Internet services

Some Internet phone companies like Musimi will forward voicemail messages as email attachments so you can listen to them at Internet cafés when travelling. This is also part of the package at some of the VoIP carriers (along with the standard options to forward to a regular telephone number or an Internet device).

• HolidayPhone anti-roaming SIM resells a foreign SIM card for your destination, and forward your calls made to your ordinary UK number over Internet to your foreign SIM card. That way, you stay reachable and can receive free calls on your ordinary number while abroad, and can still call at local rates.
• ekit.com allows people to leave messages on your voicemail for free using a toll-free number; you can retrieve them from the Ekit home page or pay to listen to them from a phone.