It blocks anonymous calls and any Caller ID with one to six alphanumeric characters. For example @@@@@ blocks callerIDs with five alphanumeric characters: user1, 12345, abc23, Peter.
Each @ is one alphanumeric character - one letter or one number. If you only want to block numbers, then use x in place of @
Yes, simply change X_UserAgentPort and forward in your router. No other change is needed.