AT&T and iPhone data use charges - WiFi and cellular link options
Many people have complained about unusual data usage charges on their AT&T iPhone bills -- often 10s of megabytes in one transaction, posted in the middle of the night. Here are a couple of updates based on the AT&T support portal:
WiFi vs cellular link: Connecting to a local WiFi hotspot and turning off your cellular data connection will block cellular data transmission and related charges. (Except for SMS messages, which are very small.) There are some gotchas, however: (a) If your iPhone goes 'to sleep' (the screen goes black), it will revert to the cellular data link, unless it is plugged into a charger. (b) Even if your iPhone is plugged into a charger, it will revert to a cellular data connection if the WiFi link drops, e.g. due to a momentary glitch with your internet provider or electric power supply, so.... (c) The only way to completely ensure that your iPhone will not revert to a cellular data connection is to turn it completely off. You (obviously) will not be able to receive calls, however.
Large data transactions in the middle of the night: Unusually large 'chunks' of data that are apparently sent around midnight are a related issue. You may think that you could avoid these mystery charges by making sure you have a WiFi connection running at night. A number of 'czars' on AT&T's site stated, however, that this is are simply an artifact of AT&T's billing system, which "aggregates" transactions that occur throughout the day into one summary charge, which is posted in the middle of the night. If this is accurate, the data connection(s) you use throughout the day will determine how large this 'summary' transaction will be.
Note: Our bill does not appear to square with AT&T's explanation. For example:
|39||04/06/2012||09:36PM||phone||Data Transfer||7 KB||0.00|
|40||04/06/2012||10:35PM||phone||Data Transfer||7 KB||0.00|
|41||04/06/2012||10:41PM||phone||Data Transfer||369,759 KB||30.00|
If all of the data from 6 April was 'rolled up' into the massive 369.8 megabyte transaction at 10:41pm, why are there two small transactions at 9:36pm and 10:35? We installed Onavo to try to get to the bottom of this;; I will post the results at the end of the current billing cycle.