Since I changed my sim to O2 my iMessage won't work

[Anonymous]

Changed sim an now my iMessage won't work

[Anonymous · Accepted solution]

Is it a replacement sim for the same number or a different number?

Assuming it's the same number try:

Settings > Messages > Turn iMessage off

Settings > Mobile > Mobile Data Network > Reset Settings

Settings > Messages > Turn iMessage on

This should reactivate iMessage for your number on that device.

[Anonymous]

Hi @Anonymous and a warm welcome to the community forum,

Navigate to : Settings > Messages > Send & Receive.

Ensure your Apple i.d is inputted at the top in blue.

Ensure you have ticked the " You can be reached ny imessage at" appropiate telephone number and e mail address.

Ensure you have ticked the " Start New Conversation from" and tick your mobile number.

Apples iMessage Official Trouble Shooting Guide : 

http://support.apple.com/kb/ts4268

Remember you do need wifi or O2's mobile data turned on to use imessage.

Other resets are :

Settings > General > Reset > Reset Network Settings.

Hold the Power Button and Home Button until the Apple Logo appears and then let go. Your iPhone will reboot.