If you’re switching to use the same SIM card on your iPhone to a non-Apple phone such as Android, remember to turn off iMessage before the switch. If you don’t switch the iMessage service off, you might not receive SMS or text messages someone sends you from an iPhone.
To turn off iMessage, on the iPhone that has the SIM card, go to Settings > Messages and turn off the “iMessage” switch.
If you no longer have your iPhone with you, Apple has created a “Deregister iMessage” website that allows you to resolve this issue.
Visit the site and enter your phone number and click the “Send Code” link. Apple will then send you a 6-digit confirmation code via SMS to your new phone. Enter the confirmation code into the form and click “Submit” to deregister your phone number with iMessage.