The villain is that pesky voicemail box, which may continue to rack up charges if users don’t also request to have it disabled.

“Many people have their phones turned off and thing that ‘now it can’t cost anything’. But even if you turn off your phone completely you still have to pay for charges when a person calls and leaves a message in your voicemail box,” said Andreas Evestedt from the Swedish Consumer Bureau for Telecom and Internet (KTIB) to the TT news agency.

A person who travels to the United States and receives calls to his or her voicemail box totaling 20 minutes can expect to pay up to 700 kronor ($116), writes the newspaper Metro.

The reason it can be so expensive is that the call is forwarded to the voicemail box (in Sweden) via networks in the other country.

One thus ends up paying both for receiving a call while abroad and for a call back to Sweden originating in another country, even through the call is never answered by the phone’s owner.

How expensive it ends up being depends on the country to which one travels, as well as which mobile service provider one has.

“Therefore we recommend to our customers to check into how they handle answering their mobile before the depart,” said Maria Hillborg with TeliaSonera.

Another potentially expensive device for those on vacation is mobile internet. Earlier this year a man from western Sweden opened up a bill for 55,000 kronor because his modem was connecting to the internet through a cellular tower just over the border in Norway.