iMessage has some things that are cool, and some things that aren’t. It does offer the advantage of letting you get the same message across Macs, iOS devices, but it has the huge disadvantage of being unpredictable. If for some reason your message doesn’t get delivered through iOS, you can’t control if it gets sent as an SMS, and that breaks the whole cross-device benefit. Even worse, it’s not cross platform, and some new complaints show that it can be quite annoying.
It seems that if you switch from an iPhone to an Android device, or even a Windows Phone, iMessage is not doing a good job in detecting that you’re not longer using an iPhone. Some minor cases have reported that people would send them messages, their iPhones would detect iMessage being available, and the message would get sent, but the recipient would never receive these. In theory, iMessage should switch to SMS immediately and deliver the messages through the mobile network, but now even Apple Support is confirming that there is a bug that is currently being looked at.
While this might not be a need to be alarmed, as there are a ton of other cross-platform alternatives that make even SMS texting pointless, obviously some people still prefer the traditional methods that are affected. We could assume that this is due to more than one iOS device being registered to the Apple Id, and these messages falling on those other devices, but we’ll keep you posted as Apple Support keeps admitting that there is a bug.