BlackBerry maker Research In Motion today unveiled the BlackBerry Pearl Flip 8220 for T-Mobile, moving to increase its fast-growing share of the U.S. market with its first clamshell phone, the most popular format in North America. The Pearl Flip 8220 features a chrome-finished frame surrounding its smooth, luminescent face. It features a high-resolution display on the outside, so users can preview emails, text messages and phone calls without opening the phone. A larger display on the inside let…