This term, which can be used in a method similar to saying you'll give somebody a ring, can also be used as a verb, such as to ygm someone, and it basically just means to e-mail someone. In the noun form, it means an e-mail. I first heard this phrase from iits inventor and my friend, Eric Miller.
John: Hey, I've got to go, but give me an ygm sometime and we can talk some more.
Alan: Okay, John, I'll ygm you sometime tonight.