Actually, you could use the Uplay overlay text to chat. Problem is, the messages don't really show up during gameplay, so you have to check the overlay once in a while. SHIFT+F2 I believe it was.
i am stuck with the achievement named Changing Lanes since i couldn't find a co op partner that will understand what i want lol
if someone wants to help,add me and i will play with u.
it sucks really the basic communications in that game are horrible.