Why have a phone for "EMERGENCIES CALLS ONLY"?

The past few months I have been having numerous issues - no data coverage in most places, no network and incoming and outgoing calls go blank and get disconnected often, my phone will be on and I keep receiving sms' giving me a missed call notifications from numbers that are trying to get hold of me and the worst is my phone goes on "EMERGENCY CALLS ONLY" mode for hours! I've tried switching the data roaming, cleaning the sim, rebooting my phone - all to no success! This is becoming frustrating because there's a whole lot of occasions I needed to make calls urgently and I can't!!!!!!