As of 2015, AT&T's prepaid international cellular data rates for 18 participating countries range from the Passport Pro package at 15 cents per megabyte to the Passport package at 25 cents per megabyte, according to AT&T.
The amount of data used while travelling determines the best international cellular data plan with AT&T. Obtaining the lowest per megabyte rates requires prepaying for hundreds of megabytes when selecting a package. If less data is used than planned, a traveler will have prepaid for unused data but if more data is used than planned, the per megabyte charge for going over will be higher than prepaying for a larger amount of data. The availability of Wi-Fi to browse the Web and amount of time spent accessing the Internet on mobile should be considered when determining how much data will be used during the trip.
If no prepaid package is selected, it is best to turn off a device's cellular data capabilities to prevent accidental data usage. Using cellular data without prepaying for a package in Canada costs $15.36 per megabyte compared to $19.97 per megabyte for the rest of the world.
The terms of the packages are valid for 30 days and in select countries, says AT&T. For longer trips and travel outside the participating countries, the best option is to consider plans from companies other than AT&T.