I'm confused on what you want. Like N7AS said you can't connect an IP Phone to your OBiTalk Account, but you can use an IP phone directly with an OBi ATA.
If you have an OBi2xx you can register an IP phone to it. This requires a free SP trunk on the OBi2xx.
If you have an OBi1xx or an OBi2xx without a free SP trunk, you can still use an IP phone with it. This setup requires the IP phone to be able to call without registration and a SP trunk defined on the OBi as SIP.
Some people with Cisco IP phone had trouble receiving inbound calls from the OBi.
You can also look at OBiPlus. I never used it, so I won't comment.
Azrobert, thanks for the quick response. As you noted, the information provided by N7AS is most likely what we need. We will check into your suggestion of connecting our IP phone. We will need to check the configuration of the phone to see if it does allow a call without registration. We have seen if a "registration" fails it will not allow calls. So we will some research on that.
Thanks again for the quick response it is really appreciated.