Roaming Zone - Global Data Roaming

KNOW YOUR ROAMING CHARGES:
Data roaming charges vary greatly and can be very expensive, so make sure you know what the charges will be before you leave home. If you aren't sure of the rates or if you know they are high, you should deactivate the cellular Data Roaming capability of your phone. There have been horror stories of people receiving data roaming charges in the thousands of dollars. Even though carriers claim they will alert you to any possible excessive charges, those alerts may not reach you when you are out of the country.
THE CHEAPEST DATA OPTION:
Wi-Fi is your best data option in foreign countries. It's usually available at high speeds and normally uses frequencies that are available even in phones that are not compatible with foreign cellular channels. It can be used for Wi-Fi calling apps which are Free or reasonably-priced. Remember, Wi-Fi Data transfers are usually not secure.
THE CHEAPEST CELLULAR DATA CONNECTIONS:
Foreign Data Roaming may already be included in your home wireless plan or have it available as an extra-cost feature. You may need to watch your usage when your home wireless data is large or Unlimited, and your foreign Roaming Data is capped at a different amount or charged at a different rate. An "International" or Foreign Local SIM can have a large amount of Data roaming included. Since the amount is paid in advance, you have no worries about getting surprise Data charges. Choose Among Different SIM's.
VOICE CALLS OVER BROADBAND ARE CHEAP BUT NOT ALWAYS FREE:
Some Apps allow you to make free calls over broadband, but not necessarily all calls are free. The T-Mobile Wi-Fi Calling App makes and receives calls on a broadband connection but uses your T-Mobile minutes at your normal domestic rate, which may be Unlimited.
CHECK YOUR SETTINGS:
Make sure your Settings Allow (or don't Allow) Cellular Roaming. Take your instruction manual or put the online manual in your phone's offline documents. You can also copy the address on your laptop computer to read the manual when you have Wi-Fi access. With a foreign SIM, set up you APN or broadband settings before you leave the store...or home. Sometimes you need to change your phone's settings manually. If you buy a SIM at a store, let them help you set it up. Often, you can save settings in your phone to be selected later.
BROADBAND SPEEDS VARY:
You might be pleasantly surprised at nice, fast 4G LTE speeds, but be prepared for areas with much slower downloads. Broadband speeds can be network-dependant, but just as likely is that your phone, while it may be a compatible "quad-band" model, may not include all the frequencies used by foreign carriers for data. Fortunately, even the slowest data speeds enable you to do things like send email and check your location on a map.

Wi-Fi AROUND THE WORLD:

While Wi-Fi can be found in a large number of countries, it is usually not as widely available as it is at home. Wi-Fi access can be found in private and public places but the Wi-Fi band of frequencies in foreign countries can include a larger or smaller number of channels, be located in different 'bands', and possibly none at all. The US Wi-Fi bands include frequencies at 2.4 and 5 GHz, with the 2.4 GHz channels (1-12) being the most common in foreign countries.

Since most smartphones provide Wi-Fi access you can use data capabilities in foreign countries as well as Calling and Text functions with appropriate apps installed. Keep in mind Wi-Fi connections, especially in public places, are not secure. It is not smart to send login information and passwords over an open Internet connection.

BTW, in most parts of the world outside the US, Wi-Fi is pronounced "wee-fee".