That feature is not technically available as per the way you asked your question. It can never be made available to everyone, as it requires each carrier to install infrastructure to support it (e.g., a bridge between the internet and their voice network). If a carrier has no such infrastructure nor any plans for same, then the answer to your question for that user would be "never". But, if the carrier does have such infrastructure and/or plans to install same, then the answer is "when the carrier makes it available". The carrier must push an app to the device, and the app must be for BB10, and BB10 must be ready for the app.
The only carrier for whom I've read anything about this is TMO USA...somewhere in their support forums (sorry, I saved no link) they said that it would be coming in the next OS release. When that happens is, of course, yet another question - but still one for the carrier to answer, not BlackBerry.
Occam's Razor nearly always applies when troubleshooting technology issues!
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