"call waiter please" supports the guest in restaurant to order meals and drinks.

Guests type in "Transaction number" shown in resturant on a board or table, "Drink numbers" shown in menue, "Meal numbers" shown in menue, "Table number" shown on table and "Number of guests" at table and send the order to the waiter/kitchen with the email adress of the waiter/kitchen, shown in restaurant.
For a fast transfer of the order, the guest should use the same email provider as the waiter. Works fast with gmail.
If you prefer prepayment, combine the app with an e-Wallet.

Waiters also can use it to send the order in the kitchen with their smartphone.

Advantages:
Less persoanl costs, less work for waiters.
If guests send the email to the kitchen you know their email adress for advertising.

Security features:
Transaction number (always changing).
You know number of guests at the table. You can watch (e.g. with a videocam) and check the number of guests sitting at table.
The order has a timestamp.
The order has a locationstamp, to show from which location the order is send to kitchen.
You receive the email adress of the ordering person. So if someone abuses the
app to send wrong orders, you can retrace the person with the email adress.