My iPhone 5c won't receive calls
Didn't accidentally turn on do not disturb?
Or try
1) Set Bluetooth OFF: > Settings > Bluetooth > set OFF
2) Restart iPhone 5: This step is accomplished by holding the sleep/wake and home buttons together until you see the Apple logo and then release.
Or try turning off wifi
Or try turning off 3G
There are many things that have been tried in this situation and different things have worked for different phones, this is an old thread but may still apply
iPhone 5 not receiving calls or voicemail | Apple Support Communities