> Moving to XMPP - using prosody - worked really well for messaging, but the lack of real-time notifications on Sandra’s iPhone was sub-optimal, and the lack of any notifications for incoming XMPP calls on her phone was really undesirable.

A note to android users: prosody real time notifications & calls work great combined with the "conversations" app as a client. You see "user is typing", you can transfer files/photo, video. And best of all, you can do audio video calls with adaptive quality (adjusts to your bandwidth) & auto reconnects.