I have looked through the manual but did not find a way to block calls.

Lately I have been receiving calls from 800-550-1259. It is a recorded message identifying itself as Pleasure Palace Casino with an offer to join their online gambling site. I used to only receive a call every other day or so but in the last week they have called me 28 times with 6 of those calls coming in the last 3 hours. It's getting very annoying and I'm tired of their messages clogging my voicemail.

Is there anyway to block the number on a SMT5800?