Ok, Ok we have some NOWs used as primary. A significantly higher balance is needed to have a NOW account without monthly fees. We have several types of (non-interest bearing) checking accounts that require a balance less than NOWs down to $0. At least in our market, many – not most – customers have regular checking accounts (not NOWs).
Back to the original poster’s question… as far as I know, there is no regulatory restriction on what type of account can be used as the primary for bill pay. As pointed out, if a Sav or MMA is used, there are withdrawal limits. So, if the customer exceeds the w/ds enough times they’ll get a DDA (at FAB they’ll get a NOW.)