Backstory: Recently I was on vacation with Julia and we ate an outdoor restaurant. In order for us to receive the check, water refills or any other simple request, we had to wait for the waiter to visit us and make another round trip... this was quite inefficient.
The Idea: A simple text your waiter service.
Deep Dive: You could start out using twilio and a google voice number. You would have a simple placard on the dining table instructing customers to text that number for an item or request. Each table would have a unique number or code so the waiter knows which request belongs to which table.
You could start with only a few simple prompts such as check, water and drink refill. As this improves the waiters efficiency, you can add more items.
Validation: There are apps in airports that all you to order items from the kitchen but most are one way communication with limited requests past the initial order.
Monetization: You would sell this to restaurants at a per table/seat basis. The value add to the restaurant is faster service, higher table turnover.