The UK sim card comes with a UK mobile number.
So that means if people back home call you, they will pay the cost of an international phone call. And if they send you a text, they'll pay the cost of an international text.
That might be included in their plan's credit, or they might have to pay standard international call rates to the UK.
You'll need to ask your family member or friend to ask their phone network provider the cost for them to call or text a UK mobile number.
We recommend that your family and friends back home just text you using apps such as Whatsapp, Viber or iMessage.
And if they want to call you, they use Whatsapp (now updated to include calling), Viber, Skype or FaceTime.