If the Kingdom hall has an answering machine for its telephone, there are ways of hacking into it and re-recording the greeting message for some harmless fun, or for leaving a pointer to this or a related web site.
This was done once for a toy company who sold a hand held puzzle like Rubik's Cube. The puzzle contained an official pay-per-call phone number that purchasers could ask for help in solving the puzzle. Some one re-recorded the number's message with something like "Gosh, you really must be pathetically stupid to have to call this number".
The idea for "improvement" by covert re-recording I got from someone who suggested a similar trick for "improving" rental video tapes. His idea was to rent some tapes from the "adult' section of an otherwise mainstream video rental outlet and re-record the juicy parts with clips from Disney animation. He figured that the guys who rented the tape afterwards would be too embarrassed to complain about the "improvements".