I sometimes discover that my iPhone 4S is no longer able to receive data from the cellular network, although the 3G/EDGE badge is still showing, alongside two bars. Usually I first suspect the application to have a problem, so I restart it, then go to Safari to open a random webpage. After some time with no loading whatsoever, I get the usual screen (sorry it's German, it basically says the page cannot be opened because the server won't answer):
This behavior can usually be remedied by going into Flight Mode and back - just tap once, wait for the little plane to arrive, and tap again.
So it's no big deal to get one's connection back once you have noticed the problem. Until then, you probably ask yourself why you haven't received any mails today or why nobody has answered your latest facebook poll for the last couple of hours... So especially for an "always-on" device that is supposed to push data to the user, this problem is somewhat annoying.
FWIW, I have witnessed that same behavior on my old iPhone 3G, but since that one had some WiFi troubles as well, I have always dismissed it as a minor hardware fault of this one particular device.
Has anybody else seen this on their device, and what can I do to stop it altogether? Is it a hardware fault and I should talk to Apple?