I have a 500 MB data plan and no data blocks on my account. I can access the 3G network and do stuff (mail, maps, etc.). However, after a certain period of 3G inactivity (say I'm on Wifi, or I'm in No Service, etc.), then trying to use the 3G network again won't work for me. The 3G symbol stays there in the status bar, however it won't load anything and if I wait, it will say "Could not activate cellular data network". The only fix is to restart the phone, but I don't want to keep doing that. Anyone got ideas? I've also tried Reset Network Settings and restoring my phone. iPhone 4, iOS 4.0.1, Fido 7.2 (Canada, official iPhone carrier) Update: I just noticed that I can get on the 3G data network if I use data during a phone call. As soon as I hang up, data network gone. Also, if I turn off wifi permanently then 3G Internet works fine. As soon as I turn on wifi, then turn it off, 3G no longer works unless I reboot. This post explains my problem fairly well.