Is there a way to block callers by caller ID by routing them to a non-working extension or mailbox? We have an Iwatsu ECS and the built in voicemail.

What type of trunks are you using?

Might be tough to do with POTS lines.

Its using a PRI for outside calls. The carrier said that they can't block calls for us for some reason, they didn't articulate, but that is my usual course of action when somebody makes a request like this.

Which 'built-in' voice mail are you using?

There isn't a table for blocking calls from an incoming PRI.

Depending on the voice mail you're using, caller ID can maybe slow a caller down a little.