1. It's multi-device at least when we're talking about non-phones; that's one of its better features, being able to use it from your Mac or iPad
2. You can make an iMessage account without having an iPhone; just having an email/Apple ID and some other Apple device to use it from
3. If you had an Android phone, presumably you wouldn't also have an iPhone at the same time? And even if you were using it on an iPhone, it seems like nothing stops you from being logged in on a second iPhone
1. It's multi-device at least when we're talking about non-phones; that's one of its better features, being able to use it from your Mac or iPad
2. You can make an iMessage account without having an iPhone; just having an email/Apple ID and some other Apple device to use it from
3. If you had an Android phone, presumably you wouldn't also have an iPhone at the same time? And even if you were using it on an iPhone, it seems like nothing stops you from being logged in on a second iPhone