[Serusers] Registering users please help

HI Friends, Yesterday I had given a public ip to my linux box and trying to test calls .so, in order to register the users i made the command serctl ul add <username/userid> <username@domain> like this i had added two of my friends names to the location table , but i asked one of my friend to download xten softphone and make configure but i cannot see his registration request and also he tried to make call in xten to another person it is showing call not approved both of my friends are behind NAT , but i used mediaproxy to run along with ser mediaproxy.so module and in ser.cfg it also shows that mediaproxy is from /var/run/mediaproxysocket . there is socket really exists in /var/run. And my mediaproxy is running on ip:port 81.21.33.35:25060 and i dont know whats going wrong Can any body please help me in making test calls , using media proxy Thanks in advance. With regards, Ravi.