I've seen the mandarin version of this called Sky of Love (2003), so yeah it's almost 20 years ago. It's also the adaption of Korean novel Ditto but they reversed the gender. This movie The Agreement was more faithful to the original source and has a better ending too.
Kim Yong (Yeo Jin Goo) was a senior mechanical engineering college student in 1999. In the faculty that most of its student were male, it's hard to find a girlfriend, not to mention at time South Korea was hit by monetary crisis. So when a beautiful junior Han Sol (Kim Hye Yoon) came in, it was a big deal and everyone wanted to know her. Luck came knocking at Kim Yong's door because he was chosen to introduce Han Sol to her new enviroment. Kim Yong love struck at first sight, and apparently Han Sol was too. But will it have a happy ending?!
Meanwhile, in 2022, a psychology student, Kim Mu Nee, was trying to find a stranger as her source person for college project. She tried her luck with her father's old HAM radio CB. And guess who answer on the other side? None other than our protagonist Kim Yong.
So how could a guy from 1999 had a conversation via HAM radio CB with a girl from 2022?! And is there any connection between Kim Yong and Mu Nee?! You have to see it for yourself to know the explanation.
Mesmerizing 9/10.