Four digits. But you need to build up a player base.
It is very much like poker rooms, just the female version. Men get together, they compete, as in poker. Women get together, they chat, as in Bingo.
Both bingo and poker take some time to build up.
The difference is that there is a good crossover between casino and poker room, but little crossover from casino to Bingo.
Slots players often like Bingo though, hence a lot of bingos offer slots too.