By itself, Voice over IP isn't going to kill your bandwith no. Then again, how many people are you listening to at any one time? 2,3? 5 Maybe?
Notice that I said that "if too many people start yapping" it kills bandwith SERVER side.
Because while your connection may only need to handle 1-5 VoIP streams, the server's bandwith has to handle all of them.
Still, I have to admit that Planetside does absolutely nothing for me, and I just also realised that this is the third MMO game Sony is currently working on. I DO hope that they aren't running all those servers on one single server / bandwith farm