A Device add on will apply to mobile routers, tablets, and smart watches. This is only available for cellular customers, and therefore will need a cellular plan to use this feature. If you have the 3G plan, your data is 1MBPS. If you have the 4G plan, then your data is 5MBPS. If you have the 5G plan, your data is 10MBPS. Keep in mind these lower speeds are applied to the device being added, and doesn’t restrict your phone’s full speeds.
Mobile Routers
As known as HotSpot Modems, a mobile router will allow you to connect multiple devices to your mobile router just like you can on a home/work router. Usually, the mobile router can only handle 5 devices. Keep in mind, the more devices connected to your mobile router, the slower the speed for each device as all devices will share with your data.
Smart Watch
As the name implies, this is a watch with a data plan. This could be an Android Wear watch, or an Apple Watch with a cellular capability. Personally, I don’t see the value in your smart watch having a data connection if you take your phone everywhere, but I know this seems to be important to many people.
Tablets
If you have a cellular capable tablet, you can add a data plan to your existing plan. You will not get a number. Therefore, the tablet can not support voice calls, or SMS. However, this shouldn’t matter as you would have a cellular phone for such needs. With tablet OSes requiring a telephone number, a number beginning with 0 will be used. The tablet will not support tethering.