[55555555]

I have the phone number 5555 5555 in a capital city - it's unlisted, never advertised, and still gets about 10 calls a day, mostly from babies and drunks. If you do get a number like this, and want to use it, I would suggest putting it behind an IVR and asking callers to press * to continue. We dump all the non compliant users to a voicemail, which is entertaining to listen to once in a while.

When we got the number first, it was not possible to call it from the major mobile networks as they had blacklisted it as a test number!