BitterSweet
The BitterSweet is a cell phone that Niko Bellic uses to communicate and interact with the environment. He can use it to phone for various services, such as a Taxi or call his friends. The phone has a number pad and also acts as a hand held computer, though these uses are unavailable. The BitterSweet is eventually replaced with a Whiz phone.
The BitterSweet is a parody of the BlackBerry.
http://www.rockstargames.com/IV/#?page=bitterSweet&content=interactive0