Just something that i see in most shooters, makes the game more tactical i guess...
e.g.
[Key presses] X > 1 > 3 = Enemy Spotted! B4
B4 being your co-ords...
Some other examples:
Need assistance!
Intel spotted!
Watch my back!
Just another side suggestion i just thought of right now:
When ever you throw a grenade, in the chat it says 'Grenade!'