U.K.-based analyst Dean Bubley [at left] of Distruptive Analytics posts a study that takes the stance there will be 250 million mobile VoIP (as oppposed to VoIP over WiFi-a different thing altogether) in just five years.
My read of Bubley's assertions is that this initial wave will be led by independent VoIP operators. But after they do their pioneering part, Bubley thinks carriers will recognize operational efficiencies of the mobile VoIP delivery mechamism and then jump on the bandwagon.
Bubley writes in part:
The report demonstrates that it will be the operators themselves which will be mainly responsible for the push towards VoIP being carried over cellular networks. Carriers will become increasingly attracted to VoIPo3G because it will enable them to fit more phone calls into their scarce spectrum allocations, reduce operating expenses by combining fixed and mobile core networks, and launch new services like push-to-talk and voice-integrated “mashups”. VoIPo3G also fits well with the move towards femtocells. Future generations of wireless technology – 3GPP LTE (Long Term Evolution), 3GPP2 UMB (Ultra Mobile Broadband), WiMAX – are “all-IP”, so unless mobile operators continue to run separate voice networks in parallel, they will inevitably transition to VoIP at some point.
I'm sorry, Dean Bubley, but I don't see the scenario you describe happening too soon. At least not in North America, continent of my residence. Based on behavior patterns that significantly proceed VoIP, entrenched cell carriers will go to all marketing, regulatory, legal, lobbying and statutory costs to protect the current business models they believe are necessary to protect their investments in networks as they are now.