A cell number is simply your phone number for your cell phone, provided by a mobile service provider. Think of it as no different from your landline number, except it's for a mobile device. It's tied to specific information on your device, and this information needs to match to assign the number to your phone.
For example, when you get a new cell phone, you often need to activate it with your carrier. This activation process usually involves providing them with your cell number, and they then associate it with your device's unique identifier (like your IMEI number).
