AT&T Charges for Data, Not Time
Understandably, many people believe that they are charged by the amount of time that they are on the Internet. However, AT&T does not charge for the amount of time that you are on the Internet. Instead, AT&T charges for the amount of data that gets transferred to your phone during a single Internet session.
Megabytes for Postpaid, Kilobytes for Prepaid
At the time of this writing, AT&T's postpaid customers are charged $2 per megabyte (MB) of data. AT&T's prepaid customers are charged $0.01 per 5 kilobytes (KBs) of data. One MB equals 1024 KB; so, if a prepaid customer uses one MB of data, it will cost them about $2.05 (1024 / 5 = 204.8, 204.8 x 0.01 = 2.05) -- instead of the $2 that the postpaid customer had to pay.
The Data Is Rounded Up to the Nearest Whole MB or KB
AT&T charges only for whole data units. If you are a postpaid customer, this means that your data usage will always be rounded up to the nearest whole megabyte. If you're a prepaid customer, then your data usage will always be rounded up to the nearest whole kilobyte.
You logged onto the Internet, clicked on a few links, and then clicked off. Your whole Internet session used 45.12 kB. That's nowhere near a whole MB, but on postpaid, it will be rounded to the nearest whole MB.
Data usage rounded up to: 1 MB
Data charges: $2
Data usage rounded up to: 46 KB
Data charges: $0.01 x (46 / 5) = $0.09
You logged onto the Internet and searched for and watched a YouTube video, which had a filesize of 3.12 MB. Your entire internet session used 3.42 MB. The nearest whole MB is 4 MB. To get the KB for prepaid, we will have to multiply 3.42 x 1024, which equals 3502.08, which, when rounded to the nearest whole KB, equals 3503 KB
Data usage rounded up to: 4 MB
Data charges: $2.00 x 4 = $8.00
Data usage rounded up to: 3503 KB
Data charges: $0.01 x (3503 / 5) = $7.00
Save Money with Data Packages
I'm a prepaid customer, so my experience is with AT&T's prepaid data packages; so, I'm not going to write about their postpaid data packages. However, a lot of the concepts are the same, it's just that the prepaid data packages are simpler and fewer.
This article covers only how pay-per-use data charges work on AT&T. I have another article on AT&T's prepaid data packages.