This story first appeared in the October 2007 issue of Entrepreneur. To receive the magazine, click here to subscribe.

It looks like the era of soft handoffs between cellular and Wi-Fi networks has arrived. T-Mobile and AT&T are providing the necessary network infrastructure, and by November, there could be more than 100 new cell phone models able to seamlessly switch mid-call to the clearest network, says In-Stat principal analyst Allen Nogee.

T-Mobile was the first to introduce dual-mode service with a great incentive to try it out: cheap long distance. T-Mobile's HotSpot @Home plan routes cellular calls over the internet via your Wi-Fi network at home or at any of T-Mobile's 8,500 hot spots in North America. You can make unlimited calls in North America without burning precious daytime cell minutes for an introductory price of $10 a month for one line or $20 for five (on top of your cell plan). AT&T's offering features the new dual-mode 8820 model of RIM's popular BlackBerry, but plan specifics weren't finalized at press time.

HotSpot @Home hardware is less expensive, initially, and includes the $50 Samsung t409, Nokia 6086 Wi-Fi-enabled phones and a free (after a $50 mail-in

rebate) Linksys or D-Link router. Other Wi-Fi phones and routers will work, but battery life takes a hit on phones without Unlicensed Mobile Access, or UMA--the secret sauce that manages network handoffs, says a T-Mobile representative. You also continue to burn cell minutes after a handoff. But with UMA, a Wi-Fi call started at home is still free even when you switch to cell service.

Another benefit of dual modes is improved call coverage. Modern Wi-Fi routers can reach where local cell towers can't. That's becoming more important, according to Gartner Inc., now that a quarter of all cell minutes are used at home. Ten percent of Americans--and 30 percent of Gen Xers and Gen Yers--don't have landlines.

Carriers partly owned by landline providers may not jump on Wi-Fi/cellular as quickly as T-Mobile and AT&T, says Nogee. But expect 190 million hands worldwide to be holding Wi-Fi/cellular phones by 2011.