I think there was a 555 joke in Last Action Hero. Or was it Pleasantville or maybe The Truman Show.
Of course, a geek would hand out a private IP address.
It's an interesting convention. It's also interesting when it's ignored, and there's at least a 7 digit number to try.
"eight six seven five three oh ni-e-yine" -- hey, wait, I can't find the "ni-e-yine" key...
It was Last Action Hero. Also, in the Rodney Dangerfield episode of the Simpsons, they traced the call, Wiggum picked it up and said "555... it's obviously fake!" and threw it in the fireplace.
There's a company that advertises on TV that has the 867-5309 number, and uses it in their jingle. I forget what it is, probably windshield repair or chiropractic.
Also, there was a number at the end of the movie "Sneakers" that was like one digit off, and the wrong area code, from my dad's pager at the time.
Steve Wozniak collected phone numbers after he left Apple and needed things to spend money on. He finally got one that was all seven digits the same, and he found he got a lot of calls from babies.
I told that story to Mitch Hedberg after a show. He did a joke where he wanted a number like that so he could tell people "just press 2 a bunch of times. when you hear my voice, you'll know you've pressed 2 enough." But these days you have to hit a "send" button.

Mitch had a joke about dialing those numbers to the bitter end. His example was 1-800-I-REALLY-LIKE-BRAND-NEW-CARPET.
"T is no longer harmless"? What's that about?
With traditional landlines, pressed extra digits after the original area code + seven would go off harmlessly into the void, but now on a cell phone, when you dial in the whole number and hit "send", the bogus digits cause problems.