Talk and browse. At same time. iPhone 3G

My iPhone 3G performs this task just fine as long as Im connected to an available wi-fi network or I have 3G network access.
When you say your iPhone cant perform this task, what happens when you are on a call and you attempt to access an app that requires internet access?
 PowerBook G4 17-inch/1.67GHz/2GB RAM Mac OS X (10.5.6) 7200rpm-100GB HD,  iPod w/Video 30GB,  iPhone 3G 16GB

The E sign was just disappeared and I couldnt use any internet access.
I am NOT talking about wi-fi network, by the way, because even 2G can do that.
Windows XP

I KNOW what you are talking about - do you want help or not?
You must be connected to an available wi-fi network when wanting to do so (as is possible with the first generation iPhone), or you must have a 3G network connection. The E sign means you are connected to the EDGE network, and it isnt possible to talk and access the internet at the same time when connected to the EDGE network just as it isnt possible with a first generation iPhone, which isnt a 3G phone.
The 3G sign must be available indicating you are connected to the 3G network. Other than that or being connected to an available wi-fi network, it isnt possible to talk and access the internet at the same time.
 PowerBook G4 17-inch/1.67GHz/2GB RAM Mac OS X (10.5.6) 7200rpm-100GB HD,  iPod w/Video 30GB,  iPhone 3G 16GB