There’s an annoying glitch with Apple’s iMessages on iPhones. For some people, when they turn off iMessages, and switch from an iPhone to another device, it’s impossible to receive SMSs from iPhone users. Something in an Apple database has registered their phone number and won’t release it.
Apple has had to set up a web tool to allow users to free themselves from this blocking.
Go to this page, enter your phone number, then enter the six-digit code that Apple sends to the phone via SMS. Click Submit, and this should update Apple’s database.
This has been an annoying problem for many users, and for a very long time, and, seems to have only found a way to fix it after they faced a class-action lawsuit. It’s good that Apple is fixing it, but I think it’s a bad sign that they’ve had to go the route of a special web page for users to de-register their phones. It suggests that they simply don’t have a grasp of how their own system works, which is supposed to de-register numbers as soon as you sign out of iMessages on an iPhone.