I never worked with the units myself, but I remember on the early days of my research on VOIP (two to three years ago), i was interested in finding a gateway that will work with the IP start and the dial up version.
What I found at that moment is a gateway that will be compatible with the phones, but it is not a H323 solution and the price that I was quoted was out of these world (100.000 dollars for a 2 T1 gateway).
At that point, it did sounded like the people that try to sell that equipment where a little bit out of these world.
I never heard about any compatible gateway besides that one, and I have since that worked only with H323 gateways and phones.
Unless you have a unlimited and free supply of those phones, it may be better for you to go with a H323 or SIP plataform
Best wishes.