I know there are numerous other ways to solve this problem. I'm asking about this specific solution because it applies to our circumstances in ways that all the others don't. I appreciate the helpful suggestions for workarounds, but my purpose here is not to get other solutions; I'm just registering my support for the idea of a RouterBoard product with a built-in or add-on ATA interface.
My previous gig was at a CLEC. We drastically cut costs by rolling out RB2011 as the SOHO CPE, and believe me when I say that we wished there was a 2-FXS model Mikrotik. I know exactly where you're coming from, but unfortunately, Mikrotik is not interested in branching out like that. (and I don't blame them, personally)
In general, I would try to educate our customer into using more "next-gen" versions of the things they were working with - IP-enabled credit card terminals, for instance. Credit Card over VoIP lines would always end up having a pizza place calling in at 8:30pm on Friday night because the CC terminal couldn't complete a batch. The other ubiquitous headache was title companies who faxed the entire library of congress 3 times a day..... "Ummmm, scanner + email FTW?"
Alarm lines were the other bugbear - we eventually made it company policy to only sell copper POTS lines for alarm lines