Keep connected on your Euro trip 

Smartphones are key for a smooth-sailing European trip, since travelers use iPhone and Android apps for everything from booking hostels to getting updates on local train schedules. Luckily, with a little planning, U.S. iPhones – in fact, most smartphones – can work just fine in European countries. Convert that smartphone for European use in two primary ways: buy a SIM card in Europe or purchase a travel plan through a U.S.-based carrier.

Buying a European SIM card

This is usually the cheapest way to use a smartphone while traveling in Europe, and it's pretty simple, depending on the actual phone in question.

Europe hosts several cellphone carriers, each offering SIM card and travel package deals. The best deal varies depending on the countries you plan to visit and the length of your trip, but here's an example of one European package:

Orange, a major French carrier, sells a SIM package for EUR 39 ($46) that includes the following:

  • A SIM card with a French phone number
  • 120 minutes of phone calls, good anywhere in Europe
  • 1,000 text messages, valid anywhere in Europe
  • 1GB of data transfer, throughout Europe

It's easy to refill the package online, as well, should you max out your data or phone minutes. But keep an eye on these cellphone carriers' policies – some require you to bring in your original passport in order to qualify for the purchase of a SIM package, for example.

GSM vs. CDMA phones

Still, there's a catch: European SIM cards are often accepted only in GSM phones, though some newer CDMA phones are starting to support them, as well.

GSM and CDMA are two different types of network technology. European mobile carriers all use GSM (which requires a SIM card), as do AT&T and T-Mobile in the United States. Verizon and Sprint, on the other hand, use CDMA, so phones bought through those carriers might not use SIM cards.

All iPhones use GSM technology, except for a CDMA version of the iPhone 4 manufactured specifically for Verizon and Sprint.

Unlocking a phone

To further complicate things, many American carriers "lock" their phones to prevent users from swapping out their services for a cheaper SIM package. Users can unlock their phones through their carrier or via a third party, but if they do so before their contract with the carrier is up, it can void the phone's warranty.

Once the phone is unlocked, a new SIM card should slip right in and work like a charm.

If a smartphone isn't eligible to be unlocked by its U.S. carrier and its owner doesn't want to go through a third party and jeopardize the warranty, he can pick up a cheap SIM-card compatible smartphone specifically for the trip. Retailers like Walmart and Target sell them.

Using a European SIM card

A new SIM card means a new phone number, so most travelers who go this route opt to download messaging apps to simplify that situation. WhatsApp, which uses a data connection to place phone calls and send texts, is the most popular option for European travelers.

International roaming with a U.S. carrier

Most U.S. mobile carriers offer their own travel packages, which are usually more expensive than the SIM option but also allow travelers to keep their own phone numbers and simplify the overall travel process.

Here are each major carrier's travel options:

  • AT&T: International day pass for $10 per day for unlimited calls and texts and the usual monthly data allowance.
  • Sprint: Global roaming provides free texts, free 2G data roaming and phone calls for $0.20 per minute in most European countries. For faster data connections, pay $5 per day or $25 per week for 4G.
  • Verizon: TravelPass for $10 per day for the usual talk, text and data allowance.
  • T-Mobile: One Limited and Simple Choice plans provide unlimited 2G data and texting at no extra charge in most European countries, as well as calls to the United States for $0.20 per minute. For high-speed data connections, shell out $15 for 100MB of data for one day, $25 for 200MB for a week or $50 for 500MB for two weeks.