Asterisk Strange Problem

hi, i have setup asterisk win32, now i know this is not the preferd and stable way to do this, but this is just a test befor i buy a pc for linux, to run on that,

i have setup asterisk, with a extn of 4464, now when i dial from a PSTN to my voip PSTN Number, the ext 4464 running on xlite, works and i have 2 way audio (now i have unblocked the ports in the rtp.conf) but when i connect my nokia n95 via the sip to ext 4464, and shut down xlite, the n95 will ring, but no audio or wont make calls, but will recive them just no audio, now i had this problem with xlite, untill i unblocked the rtp ports,

the problem being this, that the ports are unblocked for any lan user / wan user, and then direct to the asterisk server lan ip. so thats not the problem, there, anyone have any sujestions

many thanks

Ben

EDIT... fixed with the line in the sip.conf

nat = yes