I recently upgraded my Orange SPV C500 to an SPV M3100. However, I chose to use the new SIM card in my original C500 and I am using the 3100 on a 3 contract I have. It works fine except for texts - I can receive texts OK but when I send them I get the message "Your SMS message has not been sent because the SIM is not valid". It works fine if I move the SIM to the 3100. What's the problem here ? I know there's no point talking to Orange, they will say I have to use it in the new handset.

Tony