Juniper Research says that by 2012, phones supporting just Wi-Fi for VoIP will be dead. Even as the market grows to $70 billion, only 2 percent of those handsets will be just for WLANs. The future, Juniper says, is all about dual-mode phones that also support cellular.

North America will be the biggest market for VoFi by 2012, followed by Europe/Middle East/Africa, then the Asia Pacific region. They say to add another $13 billion annually when businesses factor in the controllers and APs needed just for voice.

A recent addition to the growing dual-mode phone market is Hewlett-Packard's (HP) latest smartphone, the iPAQ 510 Voice Messenger. This device can switch seamlessly between cellular GSM/EDGE and home or enterprise Wi-Fi networks through the integration of Unlicensed Mobile Access (UMA) technology from Kineto Wireless.

With UMA cellular/Wi-Fi handsets can integrate seamlessly and with minimal impact into a wireless carrier's existing core network infrastructure, while delivering better and more consistent service to end-users because calls can be carried over a WLAN (via VoIP) when cellular service isn't available. The technology also promises to deliver service over the type of network (cellular or Wi-Fi) that is cheapest and most available at any given moment.

Additional UMA-enabled cell phones and smartphones include the Nokia's N80 and 6136, Samsung SGH-T709 and P200, LG's CL4000 and Motorola’s Bluetooth A910.

While the Wi-Fi Alliance has certified 92 Wi-Fi phones since 2004, a whopping 82 of them support both Wi-Fi and cellular networks, leaving a mere 10 with Wi-Fi technology only.