Since Waitwhile is a web based app, your business will need a device that has the ability to access the internet.
Many smartphones with cell service can achieve this, but a tablet or computer with a the ability to open a web browser and can access the internet will work as well.
When cell service isn't an option, many businesses use WiFi to connect their devices to the internet.
Standard practice for most businesses use two tablets for their hardware (e.g. iPads) - one for a 'Check-in Kiosk' to let customers sign in and one to manage the waitlist/bookings among their staff.