Skype has partnered with German mobile carrier E-Plus, the first step in a strategy to extend its VoIP (define) service beyond the desktop.

Beginning in October, Skype's software will be bundled with E-Plus' flat-rate data-subscription plan. Initially, it will be available on Motorola handsets, but other handset vendors are expected to be added.

Luxembourg-based Skype said Germany is a key market. Nearly 3 million of Skype's 52 million worldwide users live in the country.

E-Plus has 9.8 million total subscribers and operates a third-generation network (define) built on the UMTS standard. Skype will be the only VoIP firm offering calls over E-Plus' network.

Skype is talking with other mobile carriers, as well, Skype spokeswoman Kelly Larabee said. She declined to say whether that included operators in the United States.

"We can't say specifically, but [the United States] is a market we're keenly interested in," Larabee told internetnews.com.

Financial terms of the deal were not disclosed. A spokeswoman for E-Plus, Germany's third-largest wireless carrier, was not immediately available for comment.

"The use of Skype is growing strongly," E-Plus CEO Uwe Bergheim said in a statement. "Through our cooperation we are combining the advantages of mobile and stationary Internet access."

Skype's mobile move comes amid a flurry of activity in the VoIP space. Just yesterday, Microsoft bought Teleo.

The San Francisco-based company's products allow for PC-to-PC calls, as well as PC-to-landline calls. The deal accelerates Microsoft's VoIP capabilities and sets the stage for a showdown in the VoIP-over-IM space, as AOL and Yahoo prepare to launch their respective services.