German pizza chain Joey's used to do that, and I always found it to be a mediocre user experience.

If you pay online, you know if your payment cleared right away. With these GPRS card readers, you wouldn't know until the driver has arrived, and frequently the readers wouldn't work for one reason or another. Of course, if you wanted to pay by card, you usually didn't have cash either, so then the driver would have to phone their shop and ask what to do, and it was just a general hassle.

They've since been acquired by Dominos and offer online PayPal/credit card payment and it's much more convenient.