Redirtect RTP behind a NAT


I am using the * asterisk version
As far as I am aware, I needed to have the asterisk server WIHTOUT any NAT, in order to redirect RTP streams…
ex : from a phone A to a phone B without going via the PBX

With the version 1.6… is there away to get this possiblity even if I have the PBX behind a NAT ? or I still need to have the PBX on Internet directly ?

Thanks for your help