Wireless Moves has a very good summary of just how many voice calls can travel over LTE compared to GSM, UMTS and HSPA.
The key though in reading the post is in the summary:
The numbers are stunning and offer interesting opportunities in the future. According to these numbers LTE is 10 times more efficient to transport voice calls than the current GSM deployment. That is, of course, if the voice calls are controlled by the operator and all optimizations used for the calculation are put into the game. For over-the-top VoIP, that's hardly going to be the case.
So, that means services which are not so called "on-deck" plays such as what Skype has done with Three in the UK won't see the same performance levels.