It appears that T-Mobile US Inc. is now planning to offer voice-over-Long Term Evolution (LTE) services at some point in the future despite earlier reports that the carrier may not go this route for 4G talk.

T-Mobile is currently advertising for a senior engineer of system design and strategy for VoLTE. The candidate will "focus their attention on the Design and Implementation of VoLTE," the ad says.

VoLTE attempts to define a framework for delivering voice over a network using the IP Multimedia Subsystem (IMS) core. Typically, early deployments of LTE have used the 2G or 3G network for talk, but the plan is eventually to take voice -- and SMS texting -- all 4G.

T-Mobile is checking out what technology it will use to implement voice over an all-IP network. The engineer tasked with giving 4G a voice will be conducting "lab trials" and evaluating "multiple vendor products" against 3rd Generation Partnership Project (3GPP) or Open Mobile Alliance (OMA) specifications, the carrier states.

The ad also calls for someone with "excellent knowledge" of Single Radio Voice Call Continuity (SR-VCC), a specification that would enable voice hand-off between LTE and T-Mobile's current network.

A report in PhoneScoop in February 2012 had suggested that T-Mobile would use its Wi-Fi calling client over IMS to deliver 4G voice rather than pure VoLTE. The two technologies don't appear, however, to be mutually exclusive as the current job ad calls for knowledge of Wi-Fi as well as VoLTE.

T-Mob's 4G timetable
T-Mobile hasn't talked too much about its plans for LTE beyond the fact that it will deploy it in 2013 and will test this summer with faster 3GPP release 10 equipment, otherwise known as LTE-Advanced. Light Reading Mobile has previously reported that T-Mobile is likely to initially bring LTE to 18 of the top 20 cellular markets in the U.S., including Los Angeles, Dallas, Houston, Atlanta, Washington, Boston, San Francisco, Phoenix, San Diego, Denver, Baltimore and Seattle.

When exactly T-Mobile might offer VoLTE on the new network is not yet known. Wireless rival AT&T Inc. (NYSE: T) has so far said it will deploy VoLTE sometime in 2013, while Verizon Wireless is pushing it back to late that year. The industry in general has been later than expected in deploying VoLTE because it's taken an unanticipated amount of time to agree on how the technology will be implemented.

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— Dan Jones, Site Editor, Light Reading Mobile