I remember taking advantage of call waiting tones to dump friends offline and steal their places on local multi-user BBS. Good days!
Mostly I was active in the early to mid 90's as a phone phreak and low level hacker. One of my favorite exploits to get access to /etc/shadow was symlinking it to .forward in a ordinary user's home directory. Then getting sendmail which executed as root to dump it to port 25. Then I'd send it to a friend of a friend who allegedly had rooted a cray somewhere - Don't know if that was true but he would run crackerjack on the file on a very fast machine and I'd get back a ton of passwords.
Friends and I around the world would sometimes phone phreak into a 'bridge' used for teleconferencing and talk to each other using that. Then someone would three-way a pizza delivery place in New York into the conference and we'd try to get pizza delivered to Scotland. I remember a friend 'maelstrom' who's real first name was Ewan (I never knew his full name) was unfortunately arrested by Scotland yard because someone posted a bunch of valid credit card numbers and phone cards to his BBS. I heard it was Scotland Yard's first hacking related arrest - don't now if that's true. I've googled him a lot to try and find out what happened to him but no luck.
Another friend 'aphex' in South Africa was raided for hosting warez on his BBS. Apparently three people walked into his house - a guy from the phone company, a guy from interpol and a guy from the south african police. They took all his equipment but didn't arrest him when they realized he was 16 at the time.
These arrests were the beginning of the criminalization of hacking. The real watershed was Kevin Mitnick's arrest in 1995 which really spelled the end of the 'wargames' period of hacking - when everyone saw hackers as Matthew Broderick cute.
This is a video of another friend. Later on around 1996 he got a major interview with the South African equivalent (back in the day) of 60 minutes. It was a very popular TV show and this was a big deal for him. Only the first few seconds are in Afrikaans in case you don't speak that. You can see the attitudes changing in this video - he narrowly escaped getting prosecuted by Olivetti and the University of South Africa. https://www.youtube.com/watch?v=RzKHa3BYemI
So after my two friends got arrested, I got a warning letter from the phone company and stopped what I was doing - which wasn't anything malicious, just exploring.
Here are some screenshots of Bluebeep. I think it's a later version, we were using 0.9 or something:
To make free international calls I would call a home country direct which is a toll free number locally in South Africa or another country and connects you directly with an AT&T or MCI or whatever operator in the USA. Then send a combination of 2600hz and 2400hz through the mouthpiece to put the trunk on the USA side into a kind of command mode. Then use the CCITT5 signaling system (which is basically DTMF but with different tones) to tell it to route a call for me. One of the tones - I think it was KP1 or KP2 could be used to tell the trunk to route the call via satellite or undersea cable (cable being the better quality because of no propagation delay).
Seizing trunks like this was similar to the cap'n crunch whistle which emmitted a 2600hz tone in the USA and in the 70's you could use that to seize a trunk in the USA. International trunks were different so we'd need a 2600/2400 tone. But the phone companies would put filters on the line, so you could do things like adding an additional frequency to the mix, or using 2600/2400 and sloooowly increasing the volume until you hear that wonderful 'KERCHUNK' sound and silence. Of course you're doing this as the phone's ringing and then an AT&T operator answers and is hearing giggling and these weird tones until his line just goes dead and we're routing the call.
I once routed a call through a few countries back into South Africa to my best friends house. The delay on the line was epic - like 10 seconds.
Recently I decided I miss the good old days of it being very hard to get international bandwidth, so I went out and got myself a ham license. (callsign WT1J) So now whenever I feel the need for it to be really hard to send data internationally, I jump on the HF bands and play around with digital modes, sending data to someone in australia using JT65 (designed for moonbounce) and only 5 watts on 14 megahertz. Makes bluebeep and CCITT5 seem like a breeze.
BBSes (300 baud modem on a C64 hooked up to an old 13 inch TV) -> warez -> learned 6510/6502 assembly and started cracking -> hacking/wardialing as a means to get access to computers where I could do C programming with 'real' C compilers -> found my way onto the Internet/ARPAnet in the mid-80s -> moved to Amiga (continued cracking on 68k) a reasonably 'real' computer with DICE C (Thanks Matt Dillon!), etc -> software developer.
Got away from the illegal "hacking" when it started becoming a serious thing with serious consequences and I was no longer a minor, and out of the cracking/piracy thing when I was earning good money and could afford to buy things.
There are a few people on HN with similar stories that I know of from back in the +hack/#hack/#Amiga! irc days (my handles there varied but were often some variant of my name: gfm, geo, etc).
I hung out on #phreak as pHaze.
Looking back, it was still the wild west. I remember finding dial-ins that had no logins at all and just dumped you to a shell.
I was inspired by it to write a UK-centric redboxing program on the Psion organiser. I can't remember what language psions used. It worked though, through a mix of tone generation and a little social engineering you could get free calls from payphones in the UK. I remember working really hard to figure out how to convert from the Mhz figure I needed to produce into whatever input the psion's sound API took. Fun times.
I was going to say the market's too small, but based on defcon 2013's turnout it may actually not be that small.