Time Warner Cable Inc. (NYSE: TWC) is working with Sprint Corp. (NYSE: S), BridgePort Networks Inc. , and Siemens AG (NYSE: SI; Frankfurt: SIE) to roll out a dualmode cellular/VOIP phone service to subscribers, according to Time Warner and one vendor involved in the project.

Time Warner’s dualmode service will allow cellular calls to jump from Sprint/Nextel's cellular network to the Time Warner VOIP network when the user comes in range of a WiFi connection on its broadband network. The reverse happens when the user goes out of range of the WiFi network.

Sources say the MSO will be the second U.S. operator, behind T-Mobile US Inc. , to bring a dualmode service to market.

Time Warner and three other cable operators announced a joint venture with Sprint/Nextel last November with the aim of adding wireless to their service bundles. Time Warner spokeswoman Maureen Huff says her company will begin offering wireless service on a trial basis in Austin, Texas, and Raleigh, N.C., “probably in the third quarter.” (See Cable Firms, Sprint in Fixed/Mobile Deal.)

Time Warner CTO Mike LaJoie said at a cable conference in March that his company will first sell standalone wireless service and bill for it on the Time Warner bill. The MSO will then begin integrating the wireless with its VOIP, data, and video services, he said.

Huff says her company plans to offer other converged services like “integrated voicemail” (connected to both the wireline and wireless phone services) and set-top boxes that are programmable using a cell phone.

Most agree that the real payoff of the joint venture comes in the form of service integration. Dualmode service is one way of doing that, and it might prove to be an important move in cable’s war against the telcos.

The companies are now working with Bridgeport’s network convergence gateway as the element within Siemens’ larger IP Multimedia Subsystem (IMS) solution that will orchestrate dualmode calls. Bridgeport’s gateway allows a single phone number to be used across various types of access networks, including WiFi and cellular. (See BridgePort Touts Convergence.)

Within the IMS context, Bridgeport says its gateway acts as a VLR (visiting location register). Siemens is now a global reseller of the Bridgeport gateway. (See Siemens Resells BridgePort.)

“We talk to the SIP software elements on the IP side and the SS7 elements on the mobile side, and we orchestrate these two call legs that are briefly simultaneously connected during the handover process,” says Bridgeport marketing VP Sanjay Jhawar.

“And there’s a lot to do with the registry for the authentification of the subscribers on both sides, and in that case we work with other IMS elements provided by Siemens and others,” Jhawar says. Chief among these IMS elements is the HSS, or home subscriber server, which acts as a master identity database for callers on both fixed and wireless networks. (See BridgePort Touts IMS First.)

Once that’s established, calls made to the mobile phone number can be delivered to various endpoints including WiFi endpoints, dualmode phones, or soft clients on PCs. The Bridgeport server also reports call data to the billing systems of both the wireline and wireless service provider. Jhawar says the whole process works according to an emerging 3GPP standard called “voice call continuity,” which covers seamless handover in IMS.

Bridgeport estimates that 30 to 40 percent of Time Warner subscribers’ cellular calls can be converted into VOIP calls, which can be delivered at about a third of the cost.

“The cable companies will have a very competitive wireless offer because they’re going to get the cost benefit of some 35 to 40 percent of the calls that they can deliver over their own infrastructure at lower cost than the wholesale purchase cost from Sprint,” Jhawar says.

Siemens VP of NGN Networks Dana Rasmussen says the converged solution his company is building for Time Warner could be used with any cellular provider. Rasmussen was hesitant to talk about Time Warner’s specific rollout plans for dualmode service. He declined to say whether Siemens engineers were working directly with Sprint/Nextel engineers.

Sprint/Nextel spokeswoman Melinda Tiemeyer says dualmode phone service is a likely product of her company's joint venture with the cable guys, but, she says, the service probably won't roll out until 2007.

— Mark Sullivan, Reporter, Light Reading