I remember 20 years ago, my dad signed up with 0060, 007, 008 and 009 and wrote a long list of strict rules about which company to use for which country and at what time. This was too difficult for me to process so I just asked him who to use before I made a call...
Then his mother (my 嫲嫲) came over to stay and dialled 001 by default, spending $65 in 5 minutes.
I still remember how to sing that silly TV advert by a phone company which also offered lifetime free dialup internet....
I have a funny story about how my cousin (who also ran a telephone company back in the day) tried to defeat Li Ka-Shing, but I don't think it should be posted publicly.