Unfortunately, OBi HTTP authentication works only on the ObiTALK protocol, which the Cisco phones can't speak. However, if the phones and Obi are on the same LAN, you shouldn't need authentication, provided that the ports involved are not open to the Internet. If your router can't ensure that, you can gain some security by using an obscure port and a long pseudo-random user name.
Uses for such a setup:
1. If you have a POTS line or a locked service that offers a POTS interface (cable, fiber or VDSL voice, Vonage, etc.), the OBi enables you to use IP phones with those services.
2. You can use IP phones with Google Voice and/or the OBiTALK network.
3. You can use IP phones with Dock-N-Talk or similar.
4. If you have a SIP service that does not support multiple registrations, OBi permits you to ring multiple phones and have concurrent incoming calls.