Apple this week provided troubleshooting steps for iPhone owners who are unable to activate iMessage with a phone number in iOS 26.
According to Apple, some customers might not be able to activate iMessage with a phone number if there is an inactive SIM or eSIM with the same phone number as an active SIM on the iPhone.
Customers who are experiencing this problem will see a "Not Delivered" alert for sent iMessages, and iMessages won't be able to be received. Messages will be sent and received via RCS or SMS, and will have green bubbles instead of blue bubbles. Alternatively, iMessages might be sent using an email address instead of a phone number.
To get iMessage to work in that situation, users should remove the inactive SIM and attempt to reactivate iMessage. Deleting a SIM that's not in use can be done by going to the Cellular section of the Settings app, and deleting the inactive SIM if there are two displayed with the same phone number.
If the inactive SIM is a physical SIM, it should be removed from the iPhone. If the inactive SIM is an eSIM, it can be deleted from the Cellular interface. After the inactive SIM has been removed, iMessage can be activated by going to Messages, tapping on Send and Receive, and tapping on the displayed phone number.
