After updating to iOS 26, some people may find that iMessage no longer activates with their phone number. This usually happens if your device has both an active SIM and an inactive SIM using the same number. Apple says the solution is to remove the inactive SIM and then turn iMessage back on. You should now be able to tap your phone number to reactivate iMessage. After this step, iMessage should begin working normally again, sending and receiving blue bubble messages with your number instead of defaulting to email or SMS.