How do you connect multiple VOIP phones behind NAT router?

I am trying to set up 3 samsung ITP-5121D VOIP phones behind a NAT router.  All the phones will connect to the remote system which is a samsung officeserv 100.  The system is connected to the internet through a public ip address on a DSL circuit.  The problem that I am having is that whenever I try to place a call from more than 1 phone at a time I don't receive any audio.  The phones use UDP 6000 and UDP 9000 to communicate with the phone system.  How do I configure the router to have all 3 phones use the same ports through NAT.
sputnik1100Asked:
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grbladesCommented:
Those are strange ports to use for a VoIP system. What protocol does it use?
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sputnik1100Author Commented:
These ports are UDP
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grbladesCommented:
Sorry I meant what voip protocol.
For example sip, iax, skinny, h.323
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sputnik1100Author Commented:
h.323
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grbladesCommented:
h,323 is fairly old. Have a look at http://openh323proxy.sourceforge.net/faq.php and you should be able to setup a proxy server for the phones to use which should solve your problems.
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