iPhone help?

I just got a new iPhone 3gs yesterday and the guy at AT&T said that it may take a few hours for the internet to kick in. Well that was yesterday, and it's still not working. I can connect to wifi and everything works fine, but when I turn wifi off nothing will load.

The AT&T store doesn't open for another hour so I figured someone on here might be able to help me.

I've gone into the settings and 3G is enabled. I've also heard that reseting network settings will work but someone told me that it will make you not able to use wifi after that.

I would greatly appreciate it if someone could give me some help. Thanks in advance.