Stretching the term "mobile phone" a bit
but if by mobile phone as in "a phone you don't have to be at home to use", then I might be able to lever 'telephone box' into the qotw.

During the first year of college, part of our clique was Tracey, the Australian exchange student who was over her for a full year. Anyway, after she went home, we kept in touch. My mate phoned a couple of times, but it was expensive.

This was back in the days when phones still went clickity-clickity when you dialed, and only a few landline customers had phones that beeped. So, my mate bought a tone-dialer, just for the novelty rather than for a genuine purpose. It was an address book that would beep phone numbers. You held it to the phone, got a dialing tone and it would dial the number for you.

Anyway, I managed to glean a scrap of information restricted to the use of telephone engineers. It allowed an engineer to make a call from a phonebox without having to insert a cash. You used a tone-dialer and after it beeped the number, you keyed in '66' on the keypad.

I mentioned this to my mates and we trooped off the a phonebox to test it out. My mate whips out his tone-dialer, beeps out the number, keys in 66 and waits. There's some clicking and then it starts ringing. Bugger me it worked.

We chatted to Tracey for almost an hour, before she said it was getting late and had to go to bed. It never occurred to us to consider the time difference when calling Australia.

It only worked the once though. I assume when someone came to empty the cashbox and didn't find it full of pound-coins, checked the logs and realised what had happened, the '66' code was either removed or changed.
( sandettie light vessel automatic New Twitter - @bollocksreally, Tue 4 Aug 2009, 13:36, 2 replies)

follow on call..
back in the day if you found a box with a 'follow on call' button instead of whatever else the button said (redial maybe?) you could put a quid in, make a call and just before the quid ran out press 'follow on call' an then something like #99# (can't exactly remember but it had a 99 in it!) and your quid would drop back out the coin return.

Used it many times back in the day
(Titanix, Tue 4 Aug 2009, 22:52, closed)

It's called Phreaking ;)
There's several tones that do different things on different telecom systems. People used to rig up "preset" tone boxes, the blue box being the most famous. Although the "Crasher box" was one of my personal favourites - imagine phoning up and abusing your enemies, only for them to find out that THEY'RE paying the bill ... priceless :D
(OvahLairD Whats a delivery tree ?, Wed 5 Aug 2009, 21:22, closed)