I personally feel that voice chat is an invaluable asset for any team based game. It allows people to convey specific and detailed messages quickly without having to simplify it for typing.
For example; In an RTS game i may want to tell my teammate to patrol a specific location on the map and prepare a defense for against a specific strategy. Typing this out would either force me to spend time writing out a long message or require me to leave out details for sake of brevity. Speaking directly to the person allows me convey the exact message i want in a timely manner that is much more easily understood and simplified.
Although I fully agree with the use of voice chat in team based games, I also notice that ingame VC's tend to not work near as well as they would need to in order to be fully effective. At times the volume is not consistent, or the push to talk key has a very laggy response. These problems with ingame VC's do make typing more prudent unless a 3rd party program is used.
If it could be done well, the option to use ingame voice chat might be a nice addition later on down the road. Certainly not necessary for release.
"War is glorious to those who have no experience of it"