Plug an ordinary telephone into one of your home's interior phone jacks. Pick up the handset and press a touchtone key. Do you hear anything? If so, it's still connected to the phone company. If not, you've disconnected it. You can now simply plug a modular phone cord from the OBi to one of those phone jacks, and, if the house wiring was done properly, all the jacks should now have a dial tone from the OBi.
NOTE: if you have an alarm panel (fire/burglar alarm), you must take additional, and more complex steps.