Alberto,
Based on the 200 OK you included, the end-to-end ACK from Asterisk to Kamailio would be expected to go to 192.168.0.170:8002 and to have a request URI of
sip:110@PUBLIC.IP:5066
This is precisely where Kamailio will try to send the ACK. Does sending it to PUBLIC.IP:5066 not cause it to reach the phone?
-- Alex