we know from experience that the reliable voice communication systems are guild oriented, not actually from the MMO side. have to remember , ESO devs are not telecommunication experts etc.
also as a sidenote, as we know how bad the MMO coms are to date, we can safely say that it would be more bright to use all that money from that "service" to the actual increasemant of content for us all. (would be actually something we all use).
i know i will use our Teamspeak or Mumble server even if we would have a semi ok voice system ingame. i would not use it as all my friends and guildies use the TS/Mumble we have now.