I added the #!define WITH_NAT option, and now the call can only be made one way. RTPProxy was started like so:
$ rtpproxy -l 192.168.1.101 -s udp:localhost:7722 -u kamailio
root@kamailioA:~# netstat -pln | egrep "kamailio|rtpproxy"
unix 2 [ ACC ] STREAM LISTENING 33357 10102/kamailio /var/run/kamailio//kamailio_ctl
BTW, my entire setup, kamailio, asterisk and the phones etc. are in one private network. I think setting realtime endpoint with "direct_media=no" is pointless as all of these interactions are fronted by Kamailio.
What's going on here? Any help is appreciated.