The total geographic area covered by a telecom service provider is known as the Network Coverage offered by that network provider. Mobile phone operators provide the mobile network with the help of cell towers where communication equipment and antennae are mounted. These cell towers provide reception signals allowing the surrounding areas within range to use the network for communication via mobile phones.  

However, when you dial a mobile number, and it says "Out of Network Coverage Area", the phone is not reachable. This issue could be because any of the following reasons:

●  Remote Use: 

The mobile number dialed might be in a remote area where there are no or less cell towers.

●  Network Congestion: 

There might be network congestion at the telecom service provider. Generally these congestion problems are temporary and get resolved within a short span. 

For a reliable high-speed network join the Vi family or port to Vi and enjoy hassle-free services.