Voice comm is nice for socializing, is not essential for succesful raiding.
It's usefullness is -imo- inversely proportional to normal paying attention and gaining knowledge of the encounters.
It could be argued that it shortens the time of pre-engagement prep (in the form of tactics dispersal etc) but there are better ways to do that.
In-combat voicecomm is in 99% of situations just a distraction.
For heavily scripted repetitive encounters it's an excuse to be lazy (you should know what to do without having someone yell it at you).
For fast paced encounters with random elements, no one person (or persons) can have an overview of the changing situation and instruct on-the-fly.
On-Cue-type elements of the fight are handled much better by bossmods, than anyone "manually" cueing the raid members over voip.
I have raided with and without voicecomm for a couple of years and I can honestly say there is nothing special to be missed if you don't use it for the PvE aspects of the game.
Some of the early "clans" brought it along from Counterstrike and other shooters and it kinda became a "copy-paste" thing.
Several of the most succesfull PvE guilds (including Nihilum if not mistaken) do not use voicecomm for raiding.
Not seeing it as an in-line part of the game, I'd have to say that SkyPE, TS, Vent fit the bill nicely as an optional/parallel form of communication.
Edit:
Found the reference.
Second part of the thread pretty much sums up my experience (although I have not raided at the level these guys have)
http://www.nihilum.co.uk/forum/showthread.php?t=7275