SIP/SIMPLE message - confirmation of delivery

Good day to all.
I have Asterisk 11, and chan_sip in use.
I can successfully send and receive sip text messages between mobile SIP clients.
Because all clients on 3G/Mobile network, their ip address can change often and unpredictably.
If client send message while receiver offline or his ip has been changed, message will be lost.

Can anyone suggest any workaround to have guarantied confirmation of message received by SIP mobile client.

PS. Mobile SIP peer will reply to MESSAGE with confirmation, but how to access it from dialplan?