Being an MVNO (virtual mobile provider) is a difficult business. Ask Helio or Amp'ed or ESPN. One is bleeding cash; one is in BK; the last is closed. But many VoIP Providers and CLEC's can see where not having a mobile component for businesses and even residential can be challenging.
But I caution that MVNO is UNE-P all over again. How many CLEC's are left selling single phone lines?
The LEC's that own the cellular networks do not want to be in wholesale. (Unless their name is Sprint-we-screwed-up-with-Nextel, then, yeah, wholesale is a must to get minutes and traffic on the network, but Cingular and VZW are just trying it out to see how niche marketing works).