There's a mountain of evidence to support the theory that T-Mobile will be the first US carrier to feature RIM's eagerly awaited BlackBerry 8220, the manufacturer's first clamshell phone.

Although neither Research In Motion nor T-Mobile are confirming the news, clues point to the BlackBerry 8220 "Flip" making its way to the nation's fourth largest carrier. The first clue comes from RIM itself, which in a statement this morning listed UMA support. T-Mobile is the only carrier in the US thus far to fully embrace the technology.

Further corroborative data comes from leaked screenshots first posted by CellPhone Signal in late August, coupled with comments by RBC analyst Mike Abramsky which named T-Mobile as the carrier.

Add to this T-Mobile's previous history with RIM -- it was the first to carry the original Pearl -- and it seems as if the reports are most likely true.

To date, the smartphone manufacturer has focused on devices in handheld and 'candy bar' form factors -- the traditional BlackBerry shapes. However, with as many as 50% of all wireless phones in the US being clamshells, it only makes sense that RIM joins the crowd.

"The popularity of BlackBerry smartphones has grown tremendously around the world and the introduction of this exciting new flip phone will help extend the reach of the BlackBerry platform even further," president and co-CEO Mike Lazaridis said.

Assuming the Pearl Flip comes from T-Mobile, it will very likely support the carrier's UMA service HotSpot@Home, and also include EDGE data capability. Like most clamshells, the device will sport an external display on its face as well as the typical phone display. Both would automatically adjust brightness based on the level of lighting where the phone is used.

Altogether, the device measures 3.9" x 1.9" x 0.7 inches when closed, and weighs 3.6 ounces. The input method is the SureType keyboard which has now become a staple feature of the Pearl line, along with the trackball.

Talk time is said to be four hours, with 14 hours of standby time.

Other features include Bluetooth 2.0 support, built in 802.11b/g Wi-Fi, a 2 megapixel camera, and a browser with RTSP support to allow for streaming video. A nicroSD slot can expand capacity to 16 GB.

RIM said pricing and availability with carriers would be determined at a later date, though that date may very well be this week. Today is the first day of the CTIA Wireless IT and Entertainment show in San Francisco.