In addition to what Penguin said, not all devices on AT&T and T-Mobile (as well as other GSM carriers) support simultaneous voice and data. Reading your post, a user may think since they have a Curve on AT&T that they should be able to use data whilst on a voice call.
You must have a 3G capable phone to use this function.
__________________ The difference between stupidity and genius is that genius has its limits. When you take things for granted, the things you are granted, get taken. Even a mosquito doesn't get a pat on the back until it starts to work. Too many people miss the silver lining because they're expecting gold. [BES 5.0.3 / GroupWise 2012 HP2]