[Asterisk-Users] nat and wandering phones

[bails]

Hi all I'm looking for a solution to this problem.

*box--------internet-----------nat-----------softphone

We have potential customers who will be travelling the world with 
laptops/pda's.
They need to be able to connect to the asterisk box via ip wherever they 
are and will have no control over nat whatsoever.

I have read that STUN offers this service, but cannot picture in my mind 
how this works, especially with no port forwarding on the nat (I mean, 
how the hell do packets traverse the firewall to find the end device).

Any suggestions welcome

Cheers Bails