It would be "easier" than running TeamSpeak, but most teams run some sort of voice comms (whether it be TeamSpeak or *bleurgh* Ventrilo), plus i'd rather not have to be in LFS just to talk to my team mates.
Nice add-on, but its fairly silly to build one into LFS when the 3rd party solution works.
Also, in BF2 they used Voice Comms, and all you get is "AAAAAAH! I'm being shot!!1111" in some winey 12 year olds American accent :P