drop someone a line

(verb) make or keep in contact with someone

Example Sentence:

I’ll start the first part of the project, you start the second, and drop me a line in a few days.

Student 1: I am going back to Brazil.
Student 2: I am going back to Korea.
Student 1: Good luck to you! I hope we will meet again soon!
Student 2: Drop me a line!

The boyfriend is always dropping his girlfriend a line while they are separated.

From the Blogs:

White Collar Criminals: Drop me a line

Media:

Similar idioms:

1. don’t be a stranger
2. pick up line
3. drop an F bomb
4. a drop in the ocean
5. cross the line
6. keep in touch
7. drop out
8. take care
9. bye!
10. peace out
11. later
12. all the best
13. keep someone in line
14. so long
15. lates!