Unplug all phones and equipment from the phone jacks, one at a time until problem clears.
Equipment includes fax, computer, caller ID, satellite dish receiver, cordless phone and answering machine.
Test line by connecting directly to the telephone demarcation point (demarc) located where the telephone line enters the premise (“little gray phone box” usually found on outside of house). A flat head screwdriver will allow you to open the front cover of the demarc to access the TEST JACK. Plug a known working phone into the test jack. If problem persists, call Mosaic. If problem goes away, it could be your inside wiring or jacks.