You can drink clear sodas, such sprite, ginger ale, sierra mist, etc. Darker sodas should be avoided, because they stain the teeth. These include Pepsi, root beer, and orange sodas.
Your dentist probably told you that if you drink soda to drink it through a straw. The bad part about braces is that it makes it hard to clean sugar from the teeth.
I drank soda when I had my braces, but one thing you have to worry about is that your bare teeth can be stained by dark sodas but the covered area won't be. It can look kinda funny when you get them off.
