I recently upgraded my Orange contract from an SPV C500 to an SPV M3100. However, I decided to use the M3100 on a 3 contract I have and stick to the C500 with Orange. However, now I cannot send texts (I get "SIM is not valid"). Surely, my new SIM should work on my old phone. Have called Orange and they just didn't want to know. Is the problem because the phone is now not supported by Orange, or is it because they only allow you to use it on just the one model you have chosen to upgrade to ?