Repeated attempts to confirm or deny phone capabilities have gone unanswered by Sony, so we should not yet assume it will dial.
As a Z Ultra owner myself, I hope for the function. The new Hangouts DOES make true phone capabilities not AS important, but where I live there is quite a few places where only 2G or 3G are available. Without voice function, the Z3 Tablet Compact would be next to useless for voice calls through Hangouts in these areas.
Lets hope this is truly the next Z Ultra, but FIRST, lets push for a definitive answer!