I spent hours as a young phone phreak trying to sieze an international (phone) trunk by whistling 2600hz like cap'n crunch did to sieze 800 trunks in the US and get free phone calls. It never worked because to sieze an international CCITT5 trunk you'd use a combo of 2400/2600hz. But I did it anyway when I was bored and tried to modulate a bit of 2400hz in there - figured one day I'd get lucky.