Below, we've explained how international cell phone use works - its generally called international roaming
The majority of carriers who exist across the globe support a technology known as GSM technology (Global Systems for Mobile). This widely used technology makes it very simple for those traveling abroad to unlock there GSM phone for international use.
For those using phones that support CDMA technology, you might find it more difficult to activate your device overseas.
GSM Phones - T-Mobile & AT&T
If you have GSM phone and are hoping to use it out of the country, the first thing you’ll want to do is check whether you have the phone unlocked for roaming. Speak to your carrier about this before you travel
It's a good idea to contact your current carrier before you travel - to make sure that you are allowed to use the phone abroad, enable roaming and also to check the price of calls, texts and data in the countries you are traveling
Some carriers will allow you to use your included minutes in your current plan in countries like Mexico and Canada - not all carriers allow this though
Remember - you will pay for calls and texts sent AND received while you are abroad.
TIP - stay on wifi for data or going online - data usage abroad can be hugely expensive
Once you've confirmed with the carrier that you have roaming set up you are good to go!
Sometimes you will only be able to do this if you are on a post paid plan - check!
CDMA Phones - Sprint & Verizon
For Verizon and Sprint phone owners, these phones run off CDMA technology and are less compatible for use abroad than GSM.
Verizon phones are internationally unlocked, allowing users to activate the device with any carrier internationally that is compatible with the phones technology. This is referred to as an “International Unlock”.
What this means is that the carrier has locked the phone to the country you purchased the device in. The other CDMA carrier the operates in the United States is Sprint. Carriers like Sprint have been known to unlock your phone for international use but will not be unlocked for use on another network in the United States.
Contact your carrier to check on what you are able to do with your phone and also check the prices for calls and texts if you can use your cellphone abroad
What if I have a pre paid phone or monthly in advance plan?
If you don't have the right plan to use your phone abroad then look to buy a sim card before you travel. There are lots of companies offering this - it works like a local sim card for the country you are going to - search for global roaming on Google to find the right one for you
TIP - if you go for this option then you will have a new sim-card and a new number while you are away - so people wouldn't be able to contact you on your US number.
You need to insert the new sim-card into your phone when you arrive at your destination
To summarize, unlocked GSM phones can be used with any compatible carrier across the globe. Some CDMA phone will come internationally unlocked but will find it more difficult to find a compatible CDMA carrier worldwide.
Always check with your carrier and speak to them before you travel