According to
this article not only Vodafone, but also T-Mobile plan special data tariffs for VoIP.
Actually I don't appreciate those news at all since except for eplus no operator has blocked VoIP or IM so far, allthough those services were prohibited by their T&Cs. So if VoIP-enabled tariffs come, that would mean for regular data tariffs VoIP-prohibition will finally be enforced.