Generally, when you get a mobile connection either post-paid or prepaid plan from your service provider it comes with multiple features and facilities. Depending on the service provider, it varies from one to other. They are number of free minutes and SMS included, included minutes worth of dollar amount, international minutes, international SMS, roaming plan and data. For example a 40 dollar plan can offer unlimited local calling, 100 minutes of international calling to certain countries with 8 GB data.
Normally, this 8GB data is called non rollover data, which means you need to use that 8 GB within a month or within the billing cycle. Otherwise, you will lose this data amount. (SIM 1)
In addition, this assumes that you have another mobile plan, same as yours for your partner or kid where you will get another 8 GB. (SIM 2)
Types of Data Share Plan
There are two types of data share plans
Data Share Plan 1
When you buy mobile plan with 8 GB, the provider may give this data as shared data, which means you can get additional SIM cards to share the 8 GB data with other devices like iPad, Wi-Fi hotspot dongle / Modem. However, you may need to pay for additional SIM cards depending on the service providers. Some service providers charge only for SIM card on a monthly basis but, some charges as normal data plan model. In the later option, you may be paying 30 dollars for additional SIM where you will get 5 GB data as well, thus your total shared data pool will be 13 GB among these two SIMs.
Data Share Plan 2
You can merge those two plans as family plan and have 16 GB (8 GB + 8 GB) for your family to use where you can use 10 GB on SIM 1 (Your Mobile) and 6 GB on SIM 2 (Partner/ Kid Mobile). In addition to this, you can get additional SIM cards, SIM 3 for iPad and SIM 4 to your Wi-Fi hotspot dongle, and use the same 16 GB data shared among all four SIMs.