# File lib/adhearsion/voip/asterisk/commands.rb, line 191
        def join(conference_id, options={})
          conference_id = conference_id.to_s.scan(/\w/).join
          command_flags = options[:options].to_s # This is a passthrough string straight to Asterisk
          pin = options[:pin]
          raise ArgumentError, "A conference PIN number must be numerical!" if pin && pin.to_s !~ /^\d+$/
          # The 'd' option of MeetMe creates conferences dynamically.
          command_flags += 'd' unless command_flags.include? 'd'
          
          execute "MeetMe", conference_id, command_flags, options[:pin]
        end