Regardless of what he states his reasons are, he did say that anyone who didn't call in to the con-man Matt Slick's show was a coward. He has been given an identical challenge. By his own standards, he is a coward.
Even with all that, I don't think he should call in. Norman is a nutcase. And people want him to call in because it allows them to portray all christians as nutcases. And... I don't think that all christians are nutcases. I think they hold a false belief. But, let's face it, the only way to avoid having some false beliefs is to have no beliefs.
Now, I have said, and I maintain, that Norman is the true face of christianity. Saner christians tone it down and conceal the more bloodthirsty elements of their religion. And, in all likelihood, they do not completely embrace their religion. But they still believe the basic tenets (e.g. Jesus being needed for "salvation.")