Nuisance Caller I.D.

I've been receiving nuisance calls lately, only the caller isn't hiding his telephone number. He calls during the day or sometimes the early hours of the morning.

The caller is a man I knew from childhood who has found religion and he became motivated to explain the ins and outs of his new findings to me in order to whet my appetite but I found it all very boring, non-sensical and stifling and as time went on he became more and more intense about it so I decided that I didn't want to speak to or listen to him anymore.

I can't understand the reason why he chooses to call and hang up. I find it all quite creepy actually but I guess it's better to know who's calling as opposed to not having a clue!