The fixed/mobile convergence services that many telcos have been launching using Wi-Fi-enabled voice-over IP phones may be giving the mobile industry a glimpse at its future, and it's a future that still may frighten traditional mobile players. That's because VoIP's free/low-cost economic model could do in wireless just what it has done in wireline — shake the crusty economic foundation of a mobile industry built around price per minute and minutes of usage.

Infonetics Research predicted a few months ago that market for revenue from Wi-Fi-enabled handsets could hit $3.7 billion by 2009. Also earlier this year, a survey by ON World suggested that there will be 100 million mobile VoIP users worldwide by 2011.

Some of those mobile VoIP adopters will be carrier customers using carrier networks, but who still get the economic benefits of mobile VoIP. Sprint recently began an upgrade to CDMA EV-DO Rev. A technology that allows lower latency and higher uplink bandwidth rates to support packet-based voice over its network — Sprint isn't launching mobile VoIP just yet, but the capability is there. Also, vendor Airvana, which has worked with several CDMA carriers, established a VoIP lab, which just last month completed a quality-of-service-enabled, mobile-to-mobile VoIP call over its Rev. A equipment.

But another part of the beauty of VoIP is that users with Rev. A phones, Wi-Fi-enabled FMC phones or any mobile device with a session initiation protocol (SIP) client don't have to wait for a traditional carrier to formally launch mobile VoIP service. They can simply download handset clients from Skype or another VoIP company to make VoIP calls that bypass the traditional cellular network.

Ron Wells, manger of product marketing for Sprint's mobile broadband service recently told Telephony's Wireless Review that Sprint won't try to block users from doing just that, but not all mobile carriers may feel the same way.

“Mobile VoIP can be cannibalizing, so do [mobile carriers] embrace it or do they fight it?” asked Bill Tam, CEO of EQO Communications, a firm offering VoIP and instant messaging as part of its mobile social networking application.

Tam said the key to carrier acceptance of mobile VoIP lies in “lowering the friction it causes and making it part of a revenue-generating packages. You have to make it work inside the carrier framework and not against it.” To that end, EQO — pronounced “echo” — created an offering that extends Skype service to hundreds of mobile handset models already on the market and using a proprietary SIP signaling solution to allow VoIP calls over existing circuit-switched mobile networks.

“This application can prove that mobile VoIP can be more about enhanced calling than cheaper calling,” Tam said.