imessages and read receipts In what situations will a message just say delivered but not read? Like if they blocked you number or deleted all messages before opening it. things along those lines?
Other than they didn't actually open it yet - reading on the lock screen doesn't tag it as read - most likely is they switched off Read Receipts for some paranoid reason.



Either that or you're blocked - there's no way to tell that, unless you ring them &amp; get bounced straight to voicemail every time… though their phone could be off.  

Blocked messages are sent &amp; arrive at the receiver's phone, but are just never shown to them, so as far as the system &amp; carrier is concerned, everything went as planned.
Voice calls might ring once, then go to voicemail; depends how quickly the phone reacts to the block. Again, as far as the system &amp; carrier is concerned, everything happened as it should.

Last option, they sold their iPhone, bought a droid, &amp; forgot to switch off iMessage. [long shot]