If the UK was to leave the European Union with no deal, the popular "roam like at home" legislation, which allows holidaymakers to enjoy the same costs for using their mobile phone abroad as they would at home, would no longer be protected under UK law. Providers would be free to charge what they wish.
From 15 June anyone can use their bundled texts, minutes and mobile data anywhere in the EU for no extra charge. The new ruling is an EU regulation, which is effectively a Europe-wide law. This means all UK providers, from the biggest to the smallest, must adhere to it.