I looked into a number of different approaches for calculating cellular data use. Each of the big American carriers offers an app or web tool for monitoring data consumption. But I recommend against those solutions because in my testing, they were generally time-consuming or poorly designed.
Instead, the quickest way to monitor your data use is by simply using your phone. Each carrier has a hidden code that you can punch into your phone to get an update on data use.
For AT&T subscribers, the method is simple. You place a phone call to *DATA# (*3282#). AT&T will send a text message showing the amount of megabytes you have used out of your monthly allotment. It showed that so far this month I have used 464 megabytes out of 3 gigabytes.
[...] Similarly, Sprint customers can send a text message containing the word "Usage" to the number 1311 and get a text message with a data report. T-Mobile subscribers can place a call to #WEB# (#932#) to receive a quick data summary.
(Score: 1, Insightful) by Anonymous Coward on Monday December 28 2015, @09:06PM
I've been on T-Mobile's unlimited plan for a couple years now. No limits/overage fees. I do get throttled once in a while when there is a lot of local traffic, but it's usually very brief (1 or 2 minutes). It's faster and more reliable than the cable/DSL service that's availble in my area, so I use my phone's data plan as a WAN connection when I'm at home. The only use I have for data usage stats is for teh lulz at the end of the biling cycle. It's not uncommon for me to use over 100 GB in a month.