Good Morning,
I must admit I am not entirely clear on what you are trying to accomplish, but perhaps I can clear up some things.
Generally speaking the Cisco ITP emulates the functions of a STP (Signalling Transfer Point) in the traditional SS7 network. What this means is that the ITP only handles the signalling portion of the SS7 network. It cannot terminate bearer(voice) traffic on it directly.
So getting back to your question, you would generally be connecting an ITP to a traditiona STP, another ITP, or a SSP (Signalling Switching Point).
You would not be connecting an ITP directly to a "traditional" voip gateway.
You can find more information on the ITP at the following link.
http://www.cisco.com/en/US/products/sw/wirelssw/ps1862/index.html
From the sounds of what you are trying to do, you may need to look into our softswitch prodcucts which include the PGW2200 and BTS10200
PGW2200:
http://www.cisco.com/en/US/products/hw/vcallcon/ps2027/index.html
BTS10200:
http://www.cisco.com/en/US/products/hw/vcallcon/ps531/index.html
I hope that helps.
Ademola