Originally Posted by hill60
You turn it off it stops working...
I think you're letting the fact that she switched to an Android-based device cloud your judgement.
I just disabled iMessage on my iPhone, waited 5 minuted and then had someone send me an iMessage to my phone number. It got sent as an iMessage as expected. This shows that turning off iMessage on your iPhone does not remove the phone number as an address from your iMessage account on the iMessage server.
Of course, I also have my phone number as a valid iMessage address on my iPad and Mac so I disabled the phone number as a viable address on each of those. I already use my @me.com address as the number for sending so I didn't have to switch those other. I waited 5 minutes and had another iMessage sent to my phone number. Still the same blue Send bubble, not the green for SMS.
This is what I expect would happen because there is no reason for iMessage to automatically assume that I don't want to still use iMessage simply because my device is logged out, which could be a variety of reasons from a password change to a stolen or lost device.
It's an oversight by Apple which makes this Apple's fault. I don't think they should be sued over it but I also don't think we should irrationally vilify someone that switches to an Android-based phone even if we can't fathom that as an upward move.