If you can't activate iMessage with your phone number in iOS 26
When you update to iOS 26, you might not be able to activate iMessage with your phone number if you have an inactive SIM with the same phone number as your active SIM.
If you can't activate iMessage with your phone number after you update to iOS 26, you might encounter these issues:
iMessages fail to send with a "Not Delivered" alert and can't be received.
Text messages can only be sent and received as SMS/RCS messages that appear as green bubbles.
Messages are unexpectedly sent using an email address rather than a phone number.
The same phone number may be displayed twice under Settings > Apps > Messages > Send & Receive.
To fix this issue, remove or delete your inactive SIM.
Remove or delete an inactive SIM and activate iMessage
In the Settings app, tap Cellular.
If there are two SIMs displayed that have the same phone number, find the one that is no longer active. If the inactive SIM is a physical SIM, remove the physical SIM. If the inactive SIM is an eSIM, tap Delete eSIM to remove the inactive eSIM.
After you remove the inactive SIM, return to the Settings app and tap Apps.
Tap Messages.
Tap Send & Receive.
Tap the displayed phone number to activate iMessage.
Learn what to do if you are still unable to activate iMessage or FaceTime on your iPhone.