Unless a user is actually frustrated with something, they won't bother investigating how to fix it. Most of the time they probably won't even know there IS a fix unless someone tells them.
Users aren't going to want to use an iOS only messaging service, and they certainly won't want to use two different services depending on who they're messaging. This has already happened before with FaceTime; some people used it and found it interesting but there was no mass appeal because not everyone has an iOS device.