Eight months after SBC (AT&T Inc. (NYSE: T)), BellSouth Corp. (NYSE: BLS), and Cingular Wireless chose Lucent Technologies Inc. (NYSE: LU) as their "IMS partner," sources say the "new AT&T" is testing IMS gear from other vendors to enable dualmode calling.

Lucent announced ts IMS contract wins at the AT&T companies last October and November. (See Cingular Picks Lucent for IMS, SBC Picks Lucent's IMS , and BellSouth Picks Lucent for IMS.) AT&T says Lucent is still its main contractor and integrator for its IP Multimedia Subsystem (IMS) network, but sources close to Lucent say the vendor doesn't yet have technology capable of initiating and orchestrating a dualmode phone call.

That's a troubling sign, given that dualmode calling, which would allow callers to switch seamlessly between cellular and WiFi networks, is among the first and most important FMC (fixed/mobile convergence) services that the new, consolidated AT&T is likely to launch. Indeed, AT&T's acquisition of BellSouth is primarily driven by a desire to leverage Cingular Wireless to launch such services.

The Lucent device that manages the handoff of calls between wired and wireless networks is called the "Lucent Feature Server." Other IMS elements like the call session control function (CSCF), home subscriber server (HSS), and media gateway control function (MGCF) also play roles in dualmode sessions; but those elements are used for numerous converged applications, not just dualmode service.

Sources haven't pinpointed where the specific technology problem lies, but AT&T and Cingular, they say, are now testing IMS technology from other vendors to initiate and manage dualmode calling.

“What we’re being told is that Lucent is not close to being ready to go to market with this stuff, particularly on the hand-over side,” says Sanjay Jhawar, marketing VP at BridgePort Networks Inc. , a Lucent competitor. (See BridgePort Touts IMS First.)

Jhawar says other suppliers including Siemens AG (NYSE: SI; Frankfurt: SIE), Nokia Corp. (NYSE: NOK), Nortel Networks Ltd. , and possibly others, are competing for second-supplier status at AT&T. BusinessEdge VOIP consultant Yaron Raps says he’s now providing consulting to some of the companies involved in trying to unseat different parts of Lucent's IMS solution. He adds that AT&T is now testing IMS technology from multiple vendors other than Lucent.

AT&T doesn’t deny working with other IMS vendors, but also won’t say if any IMS RFPs are still out there. “We are right now working in the labs looking at different IMS capabilities and services -- that’s a big focus for us right now,” says AT&T spokesman Wes Warnock. “We are working with Lucent on the IMS features, but beyond that I can’t comment."

Lucent spokesman Mike Alva says his company is working with AT&T but declined to comment further.

— Mark Sullivan, Reporter, Light Reading