Sony Ericsson Xperia Ray ST18a running Android 2.3.4 Originally on Telecom’s “Skinny”. (Bootloader is “locked”). Paid $30 network unlock fee to Skinny.

Installed Telecom “XT” SIM card. ‘Phone did not ask for unlock code. Setup apparently straight-forward, including able to download Telecom internet settings (APNs etc) automatically.

However Voicemail number (ie dial “1”) shows as +64204864236 which is Skinny’s number.  Attempted to edit number via  Settings> Call Settings>Voicemail settings  to Telecom’s +6483083210 result is error message “Call settings error Voicemail number change unsuccessful ...” and number remains as Skinny’s.

Swap to 2degrees SIM card, no problem, asked for unlock code, accepted. Voicemail number is correctly 2degrees with no intervention on my part.

Switch back to Telecom SIM card: Voicemail number back to Skinny’s! (Not even stuck at 2degrees number). Tried other experiments such as setting to Telecom Voicemail number without SIM card present, but on insertion of Telecom SIM card it switches Voicemail number back to Skinny.

I have talked to *123 and Telecom Willis Street Wellington Help desk as to whether it can be provisioned in some other way but no progress.

Anyone got any insights? Is it something to do with Skinny & XT being on the same platform?