Martin Lewis told customers to check their mobile phone contracts before travelling abroad as three companies have reintroduced roaming charges.
The charges relate to calls made in mainland Europe and have been reintroduced after the UK left the European Union.
While many people may have gotten used to not having to pay extra for calls while on their holidays, the return of roaming charges could add up and cost quite a bit.
Speaking on ITV on The Martin Lewis Money Show, the presenter warned that people could be charged £2 a day depending on their contract.
He said: "While we are out of the European Union mobile roaming charges are being reintroduced for EU travel. They are going to charge £2 per day to give you your monthly allowance - Vodafone, EE and Three - and you can see when they start, January for Vodafone, March for EE, and May for Three.
"But this only applies if you have renewed your contract or joined between those dates between July and October.
"So one way to avoid this is when your contract comes to an end, just let it keep running without renewing. Of course, the problem with that is you might be missing out on getting a cheaper deal for normal UK calls but it would prevent the roaming so you would have to do the numbers on that."
However, not all service providers have reintroduced roaming charges, meaning if you frequently travel there could be a better deal out there.
Martin explained: "You could of course Switch to O2 which is not on that list but it may soon be about to announce it coming in, as could other networks. If you are a really regular traveller, if you go to one country maybe get a sim for that country, if you go to many maybe get a global roaming sim."
