That holy grail of wireless/IP convergence, the seamless handoff of a dual-mode phone call from a Wi-Fi network to a cellular network, is still a rare phenomenon in most places. But we are taking small steps towards it now, in the form of a new class of specialized Wi-Fi access points designed to support voice-over-IP. Connected to a VoIP network and phone service, these access points provide VoIP's cheaper services to cellular phone users within range of their Wi-Fi transmitters. They may also offer better-than-cellular indoor coverage.

If the user leaves the zone of Wi-Fi coverage, and if (but only if) his or her mobile operator supports such services, these devices will also hand off calls from Wi-Fi to cellular. Motorola's recently-announced RSG system, expected by late this year, exemplifies the trend.

"If such products prove successful," says Philip Solis, senior analyst of wireless connectivity research at ABI Research, "it will validate the idea and the importance of voice-over-Wi-Fi. Even a system providing a limited service, without operator-supported handoffs, offers rewards in the form of cheaper calls and better indoor coverage."

If these VoIP/Wi-Fi access products enjoy considerable market success, that would also support analysts' forecasts of a boom in dual-mode cellular/VoWi-Fi devices.

But much work remains to be done by all industry stakeholders to arrange how services are charged and minutes billed, before seamless handoffs become an attractive proposition to most carriers.

Solis adds, "ABI Research would urge mobile operators who lag behind in offering converged services to pick up the pace, or risk losing revenue to their nimbler competitors, or because their customers find lower-cost workarounds."