How to get around NAT on mobile phones while using 3G?

Question

I am wondering how can I make real time data exchanges on mobile phones like whatapps, viber or skype do on phones. Until now I managed to make a server work on my android phone with web services but it works only with a wifi network as when we use 3G or edge connections, we have private IP Addresses and I can't be joined when using 3G. Of course I can buy a public IP address but I didn't have to when I use viber or whatapps, so I guess there is a solution.
So my question is how to get around those NAT (Network Address Translation) without having to make a periodic check for data?

Answer 1

Since phones can change their IP interface (and address) every few seconds, defeating NAT may not be such a good idea.

Answer 2

A bit vague question. But these apps all basically do either tunneling via external server or NAT traversal. And there are lots of different techniques available...