Banachek's 'Radio Magic' - a three CD set covers the subject. There's also 'Mental Yarn', which would need a little extra work, but is possible.
If it's a phone-in, how about asking half a dozen mates (trustworthy ones) to try and ring in. If one gets through...you're sorted, aren't you?
The Marc Paul chart (at least, the one with his DVD) has two signs missing. The only time I ever tried it, the person was one of the two missing ones. I should have checked it first, right?
