My iphone keeps saying no service?

I've taken out my sim and put it back in, and switched it off and on, but its still saying no service! I don't know what else to do?

Try restoring it in settings or itunes and if that doesn't work you might need a new sim card

I used to work for o2 and now work for vodafone and also trained on technical support, before updating any software or anything like that just make sure that the sim card is inserted propally a switch the phone on if no service perfom a manual roam, the easiest way to do this is put your phone in airplane mode. This is in settings airline mode and 'tap' to switch on, this takes your phone temporarily off the netwok leave this for a couple of mins… Then take it out of flight mode it will then search for the network and force u back into it, what this does is updates your phone in the network and should regain signal… If this doesn't work it might be worth contacting your network provider to see if any signal cell sites are down in your area… Other things to try is hold your home button and power button in and your phone should turn off and automatically come back on in around a minutes time this gives your phone a reboot… Alternatively ring your network provider and ask for the technical support help desk and they can check if there's any problems with the network, software etc… If you know anyone with an iPhone on the same network as you try your sim in there phone if it works fine it will be a problem with your phone if it dosn't work it will be your dim and may require a new one… You can also an apple store or a store for your network provider these will do fault diagnosis for you… Hop this helps you