Can't make call from different network

Hi, I am newbie to VOIP Technology and I am starting to follow videos in freepbx in a flash. This is what I did.
1- I installed PBX in a flash in virtual box
2- Configure Router for port Forwarding 5060 - 5081 & 10000 - 20000 ALL UDP
3- Access PBX through GUI and configure ASTERISK SIP SETTING for setting static IP & Codecs.
4- Configure extentions.
5- I have 2 IPHONEs “media5-fone” software, I succeeded in making a call if both phones in same network
But the problem is if I turn 3G on in one of the 2 phones and try to call the other phone which is in the same network of the PBX, I failed also the phone with 3G on failed to register to PBX server???

Also I tried Zoiper but failed.
Can somebody guide me what I have to do