Motorola has developed a phone that can roam voice calls between Wi-Fi (all three 802.11a/b/g flavours) and quad-band GSM. The product is not publicly announced, but visible on the website of the US radio authority, the FCC, which has approved it for sale in the US.

The Motorola CN620 may be the first commercial product to hand off calls between cell and WLAN networks, although there is no indication when it may be launched and by which provider. FCC approval is simply a necessary first step to launching a product on the market (and the FCC site is a very good source of information about unannounced products, such as this HP PDA phone).

The flip-designed phone includes messaging, web browsing and PIM functions, and can transfer calls from the WLAN to GSM, but has limited ability to move from the other way, requiring calls to be "PBX-anchored" to move them from GSM to WLAN, according to the ifone site.

Opinions vary on the thorny question of who will sell the device and to what market. Roaming voice traffic between local and wide area has become a hot topic since enterprise Wi-Fi vendors started to promote it , and devices like the WISIP phone (reviewed here) have allowed users to try out voice over Wi-Fi. The basic idea is for users to save money by routing calls over the Internet instead of the cellphone network.

However, the idea faces political and technical problems. Handset manufacturers such as Motorola have to create a product designed to cut the revenues of their largest customers, and Wi-Fi voice still has serious technical problems including expensive, power-hungry handsets, and a lack of quality of service.

The only announced project for WAN to LAN voice roaming, BT's Bluephone, gets round these problems by using Bluetooth's telephony profile instead of Wi-Fi, and by setting BT up as a MVNO (reseller) of Vodafone airtime.

The ifone site reckons the CN620 is "aimed squarely at the corporate market", and expects it to be bundled in carrier-based WLAN outsourcing schemes such as those promoted by Radioframe. However, discussion on engadget leans towards a consumer launch, with the device bundled with cable-modem Internet systems, allowing the cableco to deliver a mobile/home phone service.