Beware of Browsing While Listening to Music
The iPhone will let you use it as an Internet device and iPod at the same time. However, many users have noticed that Safari, Mail, and (to a lesser extent) the other Internet applications tend to become unstable when used while music is playing. In some cases, applications behave slowly or erratically, while in others they crash and return you to the home screen. In some extreme cases, applications continue to be crash-prone even after you stop playing music and it can require a reset or restore to get the iPhone functioning normally again. The iPhone updates have improved stability, but haven't yet solved the problem.