In article ,
says...
I think you will find that is the meaning of 'Emergency Calls Only'. I
seem to remember an agreement that emergency calls would still be
allowed even if a phone has no credit.

Sorry but that's not correct.

This message means "The SIM inside this phone has been denied access to
the network" - in this case becuase it had not been registered.

I think that call can also be
made using a different network if only network available is different
to the phone's own network.

That may or may not work, depending on local systems. In the UK for
example, this has only recently been "enabled."

Regards
Jon