There are two options for VoIP with this switch (that I am aware of): ITG line side or ITG trunk side.
If you only have one system, the line side will allow you to have i2004 (IP Phones) programmed on the switch. There is also a PC-based i2050 soft phone. I have not really worked with these before, so someone else may be able to add more info on those phones.
If you have any need to do trunk side VoIP, the ITG Trunk card can do that. It will need another node (ITG card) to talk to. I have worked with these off and on for the last 4+ years. Some deployments work fine, ones like mine do not.
I hope this helps some. Others I am sure have a lot more experience on the Line side of things.
Post a follow up if you need more specific info.
Scott M.