999 999
I have noticed my 3G phone when airborne and turned on sometimes has the operator logo of 999 999 displayed instead of TELSTRA.
I believe the operator logo is downloaded when connected to the service, no service, no logo.
So ... who's service am I connected to when the phone displays 999 999.
The phone still works and calls can be made and received.
This is my own aircraft and me as PIC. Never noticed any discrepancies in any Nav or GPS operations.