1) Repeatedly press 0
2) and #
3) and *
4) Repeatedly say "agent"
5) and "operator"
6) and your favorite mainstream swear word
7) Respond to a voice prompt with loud baby noises
Most systems are programmed to put you through to an operator if you demand one, indicate your frustration by swearing, or when presented with an accent that the software can't interpret (hence the baby noises).
That's one of my favourite "how to get to a human on the phone" myths. It's the same as no.7 really, or just being silent: unrecognised answer == human needed. Even a reliable recognition of digits/numbers is hard enough - noone sane will waste time to put some swearword profiles on the system... If they did, they'd probably make sure you get back to the menus instead - call center people are either allowed to disconnect you if you're being agressive, or they're so used to that, they don't care anymore ;)
Even though Mitel seems to have a patent for such system http://www.patentstorm.us/patents/6411687/description.html I could never find a product which implements that option. It wouldn't be cheap either. I don't think it exists... if anyone can prove me wrong, please do :)
Accent detection would actually be pretty hard and beyond the scope of the speech engines used in most of these applications.