Bills of several hundred from a fortnight abroad still happen, usually because roaming was left enabled by default.
First, check what you already have
Within some regions, roaming is included at no extra cost. Outside them, charges per megabyte can be extraordinary.
Many carriers offer a daily travel pass – a fixed fee per day of use. Convenient, and expensive over a long trip.
Travel eSIM
The most practical option for most people now. Buy a data plan for your destination from a travel eSIM provider, install it before departure, activate on arrival.
Typically far cheaper than roaming, works immediately, and keeps your normal number active for calls and messages on the other line.
Check your phone supports eSIM and is not carrier-locked before relying on this.
Local physical SIM
Usually the cheapest per gigabyte, particularly for longer stays. Requires a phone with a SIM tray, which newer models increasingly lack, and sometimes identification to register.
Before you travel
Turn off data roaming in settings, so nothing connects accidentally before you have arranged a plan.
Disable automatic app updates over mobile data.
Download maps for offline use, which removes the most common reason people need data urgently.
The trap to avoid
Calls and messages, which are billed separately from data. A single call answered while roaming outside an inclusive region can cost more than a day of data.
Using a messaging app over your data plan avoids this entirely.