title: A STUN and TURN server that work under 3G/4G Network
body: <p>It is very interesting that I can actually make a mVoIP service from the scratch. I finally could make a call using OpenSIPs source through SIP protocol. I used external STUN server that helps me to find users' private IP address behind NAT firewalls.</p>
  
  <p>However, the free external STUN server cannot find user's IP address to make a call when a smartphone is on 3G or 4G network. As a programmer, I won't give up to make a mVoIP service. However, I need a help at this time from you guys. </p>
  
  <p>Is there a good way to solve this problem? Thank you.</p>