Played with many MMO that has VC built in, but always ended up installing a 3rd party TS sw, and that is always because the in game VC is just too basic, and never have enough features to support a small group of people.

Some of the common things one would encounter with an active group of players -
1. Members just chatting for the sake of chatting.
2. Members looking for parties for whatever they need to complete
3. Groups already in a certain raid/instance/battle, that they need total blackout from the outside.

Just the 3 demands above, requires a somewhat advanced TS to handle, hence most groups opts out of the in game VC feature.

In addition, using a 3rd party TS, gives the added bonus of allowing you to communicate in case of a game crash.

jc