Well, with imessage being on topic, apple seems to be really terrible at changing to sms when someone is not available online — I ran out of internet data once and tried to text my girlfriend on imessage assuming it will just send an sms, and it just waited for like 10 minutes before telling me it couldn’t be sent. The other side is even worse - I would have assumed apple checks whether the other half is expected to come online anytime soon and if not, send an sms instead. Nope, you just don’t get a message and are expected to long press and send as sms manually.