mev

GSM is one of the major cell phone standards, another is CDMA.

In the US, major carriers that use GSM include T-Mobile and AT&T. Carriers that use CDMA include Sprint and Verizon. In the US, the choice of standard isn't quite as important because historically phones have been "locked" to a particular carrier - and you get charged for your phone together with your service. For bike tourists it also often matters where network coverage is found.

In the rest of the world, two significant differences include:
1) GSM is by far the dominant protocol and has the best coverage.
2) Phone service is usually not tied to a specific phone. Instead, you buy the phone separately and then get SIM cards for either a service contract (post-pay) or a pay-as-you-go service (pre-pay).

To some extent this model has then also come back to the US with increased adoption of "unlocked" phones, namely ones where you can buy a SIM card separately from buying a phone. I've seen mostly pre-pay, though believe post-pay also exists. These SIM card mechanisms can be built for either CDMA or GSM networks.

With that background, what has Amazon done with the Kindle paperwhite and similar series?
(1) They have built in support for the GSM standard into devices
(2) They have negotiated with carriers worldwide that Amazon has made one-time payments system-wide rather than requiring individual users of these devices to buy some sort of service.
In effect what Amazon has done is take a US model (buy phone service together with a device), and brought it to a world-wide audience.

The net effect is when you take your Kindle traveling in US or elsewhere, typically if there is phone service (in the US T-Mobile or AT&T - in rest of the world any phone service since they are mostly GSM), you can download and buy new books. Amazon does put some restrictions on that service - the biggest ones I've noticed is you can only use the "email to my device" option via wifi - and you can't use their (primitive) web browser other than wifi.

I have used this in both Africa and South America while camping in my tent. I finished a book and browsed, bought and downloaded a new one. Obviously if there isn't phone service then this doesn't work. However, also surprising how many of these developing regions have cell towers, in effect having skipped a large land-line network in favor of jumping directly to cell.