By Katie Marsal

Published: 09:00 AM EST (06:00 AM PST)

While its inevitable that Apple will introduce a version of its iPhone handset for U.S. wireless carriers outside of AT&T, it's T-Mobile that stands as the front-runner for the gig rather than Verizon, one investment research firm said Thursday.

In a report released to clients Thursday morning, Kaufman Bros. analyst Shaw Wu cited sources as saying that additional U.S. iPhone carriers are becoming "closer than reality than ever," with some indicating that an announcement could come as early as this fall or early next year.

"While the general consensus is around Verizon (which we believe will happen eventually), we continue to believe that T-Mobile USA is the most likely candidate given its use of similar cellular technology as AT&T," he wrote. "Also, we are picking up that T-Mobile views the iPhone as key in winning back lost customers and as such could be more likely to agree to Apple's terms."

More specifically, Wu noted that T-Mobile's 3G service (UMTS/HSPA) supports 1700 MHz and 2100 MHz frequencies while AT&T supports 850 MHz and 1900 MHz frequencies. With both the new iPhone 4 and iPhone 3GS supporting 3G at the 2100 MHz frequency, the technical hurdle to support T-Mobile would be minor compared to supporting CDMA technology used by Verizon and Sprint, he said.

Another reason why the analyst believes Apple is poised to broaden availability of the iPhone in the near term is stem adoption of mobile phones based on the Android operating system developed by rival Google. Currently a relatively niche player in the market with just 9% U.S. share, Android's progress to date is believed to be the result of a lack of competitive options from Apple on networks outside of AT&T.

"Our sources also indicate that one of the key reasons why Apple is more open to adding U.S. carriers in 2011 is to attack Android more directly," Wu wrote. " Looking at industry data, Android's wins have been where iPhone isn't available and that could change dramatically if the iPhone were available on more carriers."

The Kaufman Bros. analyst reiterated his Buy rating on shares of Apple alongside a $320 price target, saying the Cupertino-based company is best positioned "to outperform in this tough macroeconomic environment with its defensible strategic and structural advantages and its vertical integration."