I would connect everything up. Go to fax and call your cell phone on anybody who has caller ID. Verify which number comes up on the caller ID. When calling from the fax amd house number comes up I would think the jumper you are using may be a 2 line jumper. The fax may be configed to pick up the 2nd line not the 1st. If you ran a jumper straight in and not used the jack they were originally using, its a good possibility this is whats going on. But let us know what you find out.
This is CABL.com posting #163088. Tiny Link: cabl.co/mQAC