Mobile data not working after upgrading to iOS 4

Try reseting your network services..
Settings > general > reset > reset network settings

If that doesn't work.. Try turning your phone off for a min or 2.. And then turn it back on

Make sure your bill is paid...

 

Same Problem here

I'm having the same problem (although I didn't jailbreak and I've got a 3Gs). Everything is working great except for data.

Did you figure out the problem? Please tell me you found a solution as I tried the suggestion of resetting the network settings with no change.

 

How certain are you that you didn't jailbreak?

http://forums.macrumors.com/showpost.php?p=10248642&postcount=7

 

I previously had it jailbroken... is that what you are talking about? I didn't try any jailbreak after upgrading to iOS 4.

 

http://forums.macrumors.com/showthread.php?p=10253549#post10253549