Hi guys and girls, I have a three week old iPhone 4s which I got as an upgrade on my contract. I have noticed though it has gone into a "No Service" mode where I cannot make or receive calls. The only way to correct this is to restart the device. Is there a known problem on the iPhone regarding this? Or should I take a trip to an Apple store? It doesn't happen a lot - but when it does and I haven't noticed it for a few hours, I get irritated with it. R.