Aye, you have to bind the vehicle speech keys, using VOIP wont work for everyone and chat is too slow, its in the control menu allmost at the bottom.
Also, Lazerus is correct that a TT tag does not insure the player is a great tanker, but that he/she wants to become one, take me for example, im a good commander but i still need practice in the driving department.
So, i hope us TT's will make a commitment to help eachother out, give advice, and be freindly, because everytime you help a fellow tanker out, the experiance will get better for us all.
And yeah, i too think its a pretty safe asumption that TT's will also be team players on infantry maps, im not sure if that should be an official thing, but then again it could be.