Previewed at WWDC, launching in the fall.
Apple Launches Web Tool to Deregister Phone Numbers from iMessage
Users switching from an iPhone to another device were often unable to receive SMS messages from another iPhone due to their phone number still being linked to iMessage. These specific errors with iMessage have been a well-known issue since 2011, which is when the messaging service debuted with iOS 5. They were also made even more apparent this past May, where a server glitch caused widespread message delivery problems. Apple was even sued over the matter in a California court, although the company claimed that it was aware of the issue and could not provide a fix.
Apple's web tool for deregistering phone numbers from iMessage is available now.