Just like back home, cell phone networks do not always have perfect coverage. 
Wireless networks may not reach underground apartments, deep inside some stores (especially supermarkets) and even different inner rooms of an apartment.
If you are close to the Israeli border, for example, your phone may be picking up a foreign cellular network and will stop working to prevent roaming usage.

Many times you could shift locating and it will start working again.

You could also try restarting the phone and searching for the network manually.

If you are still having issues and have a CID plan you could contact us or contact your provider (other provider's contact info can be found here)

Our contact information can be found here.
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