I have had an Obi connected to house wiring for several years. It has been my experience that as long as all the jacks are part of the same line, you can feed the telephone jack from the obi into any wall jack and it should make all other jacks in the home connect to the obi phone service.
What I did was to make sure the phone co. service was "dark", and just to be on the safe side, I used several modular splitters to isolate "line1" and "line2", and I feed the obi into line2 and plug all the phones into line2 for each wall jack so that there is even less chance of the telco activating that line.
Also (this may not apply to you), I found the main entry point in the house where the inside wiring interfaces with the outside connection to the phone co., and I unplugged it, so now I have a loop running inside the house with a complete air gap, off the grid from the telco wires. It's basically like a long phone extension cord running behind the walls to each jack. It would be the same thing as if you got a 50-foot phone cord and plugged that into the Obi and plugged the phone device into the other end 3 rooms away. Only now that cord is hidden behind the sheetrock.
Hope this helps.