1. Checking the APNs against the carrier (Telstra's) APNs and they are correct
2. Created new APN with similar settings
3. Manually overridden APN settings in Textra using those supplied by carrier
4. Removing all of the default APNs and creating a new APN
None of these have worked, I just get a failed message when attempting to send or receive.
SMS, Internet etc all work OK.
Firmware not changed.
MMS worked fine before flashing to ARHD