If the technology behind this potential sea change is up in the air, the business models are even more so. Nobody's quite sure who the major players will be and exactly what services they will provide.

The cellular operators obviously want to stay in the game. Sprint's Combophone, for instance, gives that company the potential to gain revenue for in-home fixed-line voice service from its cellular subscribers. However, many smaller players are also trying to get a piece of the action.

"We're very interested in voice because it's still a killer application," said Jeff Thompson, CEO of TowerStream, an already-profitable ISP providing fixed WiMax-class access to enterprises in six U.S. cities. He said his company is particularly well positioned to take advantage of mobile VOIP.

"When you use WiMax, you have a much lower cost than legacy infrastructure, plus it's all IP-based," Thompson said. However, he added this potentially gnarly question: "Everybody likes mobility, but how do you make money with mobility? We definitely think voice is a killer app and we have to support it. But whether we do it as a partner or ourselves, we haven't decided yet."

At the other end of the spectrum is Gartner's Redman, who is less certain that there will be a lot of new players in the mobile voice game.