Be careful doing this for a service with an offline/telecoms aspect. Both my bank and credit card companies ask to verify that information when I phone them,

Chances are you can just answer "I wrote gibberish." and the guy on the phone will accept that.

Or you could just mumble incoherently.

http://www.zug.com/pranks/visa/index03.html

Unlikely. The person on the phone doesn't have the right to make judgments like that. Furthermore, if they were to allow it, that means that everyone who writes gibberish can have their account compromised by someone who guessed that it's gibberish.

Whenever i need to open an important account (say, with the power utility) I make up answers and record them on paper. Simple. Effective.

That's fine as long as you save it. One of my online financial sites asks for the answer to one of those questions every few times I log in.

Ha! I've not come across that before. Guess I'll have to stick to something made-up but memorable from now on :(

They'll get an earfull when they ask me for it though, futile or not :)