Zte Grand X In User Manual page 321

the network
Cannot
answer
incoming
calls
You cannot
make
outgoing
calls.
You are not within the
network's service area.
Poor signal.
You have activated the
Call barring feature.
You have activated the
Call barring feature.
You have activated the
Fixed dialing numbers.
Check the service area
with your service
provider.
Move to an open space,
or if you are inside a
building, move closer to
a window.
Go to Settings > Call
settings > Call barring
settings, and then
select Deactivate All.
Go to Settings > Call
settings > Call barring
settings, and then
select Deactivate All.
Go to Settings > Call
settings > Fixed
Dialing Numbers and
select Disable FND.
321