They have interested me since my childhood and even though the world has changed to blackberrys and bluetooths, the boards delivering messages still survive.
The concept of leaving a note on the board for locals regarding any social gathering, public function or religious event apart from announcements of births, deaths and associated rituals, is quite useful.
In one of the lanes in a ghetto in Old Lucknow, I have been noticing Shia and Sunni boards for years. The residents use chalk to leave the message for a 'milad' or a 'majlis' or any other ceremony.
Mostly the notes are in Urdu and sometimes in English or Hindi. Though these message boards are found in other places also, the fact that no one ever leaves a misleading message or a prank, is even more surprising.
In some cities that haven't seen huge expansion, the boards are placed at a prominent junction. Like in Burhanpur, the boards are placed at the Chowk so that every passerby gets the message about any happening. In some other places, there are drummers and announcers of unique accents using loudspeakers in auto-rickshaws to make announcements.