It’s unlikely that any mobile device will match the Apple iPhone in a gadget popularity contest, but the Palm Centro’s social calendar is filling up on its own – Palm recently surpassed 2 million unit sales, the company said this week.

A change from the high-end business orientation of Palm’s Treo series, the Centro  gained a reputation last fall as a smartphone with impressive features and specifications but at just $99.  The phone is physically small, retains a QWERTY keyboard, ships in a variety of colors and runs the traditional Palm OS.

The smartphone is now available in 25 countries from 20 carriers, including AT&T, Sprint Nextel and Verizon in the United States, company officials said.  Sprint was the first carrier to offer the phone and recently deployed a software update that improves Google Maps, Gmail, Bluetooth functions, Sprint TV and instant messaging features.