If your cable modem has Wi-Fi or more than one Ethernet port, it is a router/modem combination. You should connect the OBi directly to an Ethernet port on the modem, and you will probably have to change some modem settings. In general, try turning off anythng related to SPI, SIP, ALG, or firewall. If you can't figure it out, post make and model and perhaps someone here can help.
However, if it's just a "dumb" modem with one Ethernet connection, the switch scheme won't work anymore, because the modem will only "see" one attached device at a time. You will need to connect the Belkin WAN port directly to the modem and connect to OBi to one of the Belkin's LAN ports. Of course, you'll also have to determine why the Belkin and OBi don't play well together and fix that.
Post some details about what is wrong. Does ***1 report an IP address? Can you access the OBi's web page? Does the echo test work? What services do you have configured? Do any work? What error or message occurs when you try to call?