Your 40-year old (?!?) telephones may be the culprit. Most phones manufactured within the past 20 or so years should work just fine, using two to four hardwired telephones per line, wired in parallel (via a 1-->2 jack plugged into the OBi, or via plugging the OBi into the house wiring). Phones have an internal impedance, that, when added together, collectively consume the power applied to the line by the phone company, or in this case, the OBi device. If that total impedance is too high, you'll overload the OBi and results will be unpredictable. Get some new phones. In fact, get any decent DECT 6.0 cordless phone system with a couple of handsets, and you only have one hardwired connection to the OBi. Panasonic or Uniden would be my first two choices.
Are you the guy who was discussing running the hardware off of a 12V solar system? If so, you may also not be supplying enough current to the device, with the side effect of making it unreliable.