Have you tried http://www.openh323.org?
I must admit I have, but struggled with the documentation or lack of it.
I am interested to know if you get this one or another one working.

Mark Frater
Technical Director, Mercury Telecommunications
Level 3, The Textile Centre, Kenwyn Street, Parnell, Auckland
P.O.Box 99856, Newmarket, Auckland
ph +64-9-916-0300    fx +64-9-9160301    mb +64-21-336-598

>Message: 14
>Date: Tue, 27 Aug 2002 15:52:39 -0700
>To: rte-ascend at lists.real-time.com
>From: Nicholas Sten <nsten at o1.com>
>Subject: [Ascend] MAX TNT / APX and VoIP
>
>I was wondering is anyone has come across any open-source VoIP Gatekeeper
>products (i.e., not Lucent's MVAM) that interoperate with the MAX TNT / APX
>hardware acting as VoIP Gateways.
>
>Nicholas Sten
>Manager, Special Projects and Emerging Technologies
>O1 Communications
>http://www.o1.com
>nsten at o1.com
>916-554-2133