Which promptly failed to dial out this morning. Steven called me after a fruitless session with the credit card processor's technical support department. I said (roughly), "Duh!" and passed the phone off to daisy_knotwise who said a slightly longer-winded version of "Duh!" (Ok, she was actually a lot better than that, but unfortunately had no ideas that easily translated themselves into action.)
Later in the morning, I realized that these machines had been working a few weeks ago at Windycon. This meant that there could only be three possible answers to the question, "What the heck is going wrong here?"
Now, I had been over at Steven's a few weeks before as we sorted out the ISFiC Press taxes and while I was later helping sort out some problems they were having with their new router, Steven mentioned that their phone lines were handled by Vonage. So I called Steven back and suggested that he swing by my place this afternoon as he made his rounds, bring the machines, and we'd try them from here on our AT&T service.
He did. Everything worked fine.
A quick round of Googling explained that the credit card machine has an analog modem which gets really, really picky when you drop a packet, an activity that Vonage will engage in with fair frequency. Ok, but the machine used to work from Steven's place, so...
Well, it worked from his place right up until his old Vonage equipment was ruined by water in his crawl space (along with the router, which is why I was fixing up the configuration on the new one). And the new Vonage equipment doesn't work at all with the credit card machine.
Just as well. Apparently, the credit card machine doesn't encrypt data on the phone line, which means that you don't want to use it on a VOIP line anyway, because it's much less secure than POTS.
And, as it turns out, now we can't.
(Yes, solutions exist. We're looking into them.)