Neil A. Hillard wrote:
> That's like comparing apples and pears!  _IAX_ may well be better as I
> believe it uses a single port and plays better than SIP with NAT.  I'm
> only currently using SIP so I can't say from experience.
>   
http://www.voip-info.org/wiki-IAX+versus+SIP

Some info. You can google around for more, but it's pretty well covered. 
Don't know from experience either - most voip providers here in my 
country will either stick proprietary/confusing/crummy boxes you plug 
standard telephones into, or offer H.323 (which is NAT-hostile). *Some* 
will provide SIP if you ask nice.