Major points have been put in bold for your convenience...
I'm recalling another game a couple of year ago from Sony with integrated VOIP. The technical execution was solid, though it had some balance issues, and got a couple of rebuilds. However,
it had full integrated voice communications, and after the first couple of months, they were utterly useless. The system ran into a couple of serious issues, unfortunately, and, as a result, most players disabled the in-game comms, and either used their own 3rd party application if they were organized, or did without.
The two major divisions that these issues fell into were:
1)
Internet Problem Archetype
Simply put, many people on the internet whether intentionally or not, and for a variety of reasons, behave in fashions which can become unpleasant or disruptive under the best circumstances, and frequently can turn hostile or worse. In the game referenced earlier, examples ranged from the benign, but distracting, stoned/drunk/etc Officer-In-Charge, to the one (or occasionally more) teammates blaring some flavor of "music" (over sort sort of speaker, in some vague proximity to the mic, but ALWAYS with plenty of static and feedback) with the entire team, for our listening pleasure, to the individual who will simply NOT SHUT UP (sometimes about an actual topic, sometimes not,) all the way to the other end of the scale with the individual who was in some combination convinced of his superiority to the team, and told them so, and / or spewed a stream of verbal filth for their own reasons.
Some helpful reading, on the topic:
http://en.wikipedia....hibition_effect
http://en.wikipedia....hibition_effect
2)
Simple, (but Unavoidable) Real World Communications Issues
There are certain basic requirements for good communication, not the least of which is that the people involved a) speak the same language, and

have the technology (and other resources) required to take advantage of them. With open, integrated, automatic voice chat, there is no control over what language your teammates will speak, what quality their sound gear is, or how well it is configured, or what other Real World factors(such as background noise) will affect it.
In closing, as much as I would like to hang my hopes that universal, integrated VOIP will close the gap between PUG players, and the more serious/dedicated player base, I know better. Even if it does solve one set of issues, and there is no guarantee that it will, it will simply, and unavoidably, create a different, and possibly worse, set.
TLDR: Integrated automatic VOIP has been attempted in the past, and fails for reasons that have little to do with the provider, and much to do with the end user population.