Using firmware V5223 and tried various newer firmware up to the latest V52145 but when rebooted the modem cant find any Australian carriers such as Telstra using the original working SIM.
Also the SIM info says no IMSI after reboot.
The API settings are the same (Telstra.iph or Telstra.extranet). Tried rescanning network but no luck.
Thanks to Praveen Paul from Kapp Engineering for the successful resolution.
The Cell module turned itself off during the firmware upgrade!
To turn it back on:
Telnet into the device and runt he following CLI commands:
config 0 save
The Cell module instantly turned on and started scanning the mobile network and then logged onto the network.