You sure you were not on WIFI? Surfing the web and receiving emails can happen on WIFI when you are on the phone. You definitely cant do both (surf and on phone) if you have and just on 3G.
You can text while on the phone while on CDMA. Email and Web Surfing are a no go without wifi. It's one of the drawbacks of CDMA then again I don't have to suffer with AT&T. Fair Trade
Texting and Voice use the same channel of data, whereas data is set into another channel in the CDMA world. Problem is, the radio can only do one at a time; a GSM phone can use both at the same time.
So you can text and call at the same time, or you can use data. It's only one at a time though.