Are you addicted to your phone? I know some people who are so obsessed with their mobiles that they constantly have to check it every few minutes.

Others carry bags filled with batteries and charging cables, just in case they run out of charge while out and about.

Most people are able to apply a bit of moderation to their phone usage, but there is little doubt that we are increasingly reliant on our mobiles. Particularly when we go on holiday.

But beware! You could be in for a nasty shock on your return. Because data roaming is back – and my inbox is heaving with complaints from readers who have been left with hefty bills for using their phones abroad.

What is data roaming?

We may call them phones, but in reality, we are carrying around an extremely powerful mini computer in our pockets. When we connect to the internet away from home or free WIFI, we use our ‘data allowance’ – the amount of data you are allowed to use in internetland each month. When abroad – unless your plan allows this – you’ll pay more for this data usage. Sometimes a lot more. This is known as data roaming.

You’ll also pay for traditional mobile phone things too, like calls, texts, and sending pictures.

When we left the EU, many UK networks reintroduced data roaming charges (formally free). These tend to be around £2 a day in the EU. MoneySavingExpert has a guide to your carrier’s charges here. But in non-EU countries, you could always rack up hefty bills for using your data or phone, sometimes even inadvertently.

Regulator Ofcom found that a fifth of all holiday makers were not aware of roaming charges and a further fifth didn’t do any research on charges before traveling.

How do I avoid being charged?

While many people are aware of the concept of data roaming, it’s not often understood how it works in practice. In fact, lots of the people I speak to who have been hit with huge bills were unsure if they were supposed to leave the data roaming button on or off on their phones (the answer is ‘off’ by the way!)

Ofcom is proposing making warning texts mandatory as a way to help travellers avoid big bills. But for now, try these tips to avoid these unpleasant charges.

The simplest option is to use the free Wi-Fi where you are staying for all big data downloads, excursion planning and long phone calls. Wi-Fi abroad is improving but can still be a little flaky, so remember to check regularly that it is actually on.

Most mobile phone companies will allow you to set your own spending limits abroad – but only for data, so watch those calls and texts (particularly sending pictures and videos). You can also buy ‘add on’ or ‘bolt on’ roaming packages but make sure you speak to the supplier first so you understand exactly how they work.

Beware of planes and boats! For the last decade or so, I’ve heard from multiple people whose phones have connected to mysterious networks as they travel by boat around the world or by plane. Obviously, your phone should be in airline mode in the air, but be wary if you are cruising.

Another option is an ‘eSim’. This doesn’t involve swapping the Sim card in your phone. Think of it more as a virtual Sim that you buy, load up with cash and use with your phone. This will then give you ‘local rates for local people’ and can be much cheaper. But again, watch out for call and text charges which aren’t usually covered by the eSim. You can also just buy an actual Sim card for pay as you go abroad, though your number will change.

Switch off your voicemail. I was recently contacted by a reader who told me that she’d been hit with £150 just for receiving voicemail messages that she never listened to! Yes, this can happen. So switch off your voicemail. You’re on holiday, after all!

Martyn James is a leading consumer rights campaigner, TV and radio broadcaster and journalist.

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