It can also mean to "call someone on the telephone". Although, that is not the original meaning. I think that is because now some people think "line" means telephone line.
Examples:
I'll drop you a line when I get to the airport. [ I'll give you a call.]
or
Lyrics from the song "Drop Me a Line" by the Slycaps.
俺文化不高,似乎美剧都100%都是call me/give me a call啊。另外一直以为drop me a line都是邮件的意思。
特别同意9楼说法,对于非母语,还是用些常见有把握的说法比较好,容易说也容易被理解。
比如讲黄牛这个词,有scalper/hawker 两种说法,但后一种就从来不敢用,生怕不小心就说岔了被BS了