Build the web app portion that allows reservations to be made from the customers perspective, just like they have now. Integrate it with Twilio so that the restaurant receives an automated call and can confirm/deny the reservation on their end, without having to deal with a bunch of new hardware. You just tell them that they're going to receive a phone call with the reservation information and the options. There's little or no training required on their side, no additional hardware, minimal integration, no new systems. It's a more organic transition for a restaurant when you're trying to talk them into becoming a customer.