If you can, go to an ATT store, or any store that has BlackBerrys, and play with one - try it out and see what you think. There are plenty of apps for social networking. There are a lot of games, too. You can change the wallpaper as many times as you want, but not two on the same screen if that's what you meant.
I have an iPod Touch, but I listen to music on my BlackBerry instead. You can see the features and specs here for the 9900. BlackBerry - Bold Touch Phone - New BlackBerry Bold Touch Screen Phones - US