A few weeks ago, I got a call from a friend, seeking advice. His iPhone 4, which is on AT&T’s 200 MB/month data plan, had mysteriously racked up over 200 MB of data in just a matter of days. He was now being charged at the overage rate.
This data usage happened even though my friend contended that he had made virtually no use of the 3G network during the critical interval. He next began tracking exactly when the mysterious usage was accumulating and found that it was happening mainly at night, at a time when both he and his iPhone were asleep!
He eventually called AT&T to complain, initially thinking they would admit some sort of error and credit his account. Wrong. They contended the usage was valid and stuck by their guns. He next inquired whether they could at least tell him what app(s) on his iPhone were responsible for the overage. No, they could not. They claimed not to be able to track such information, only that the usage had occurred.
I advised him to try the AppSwitch app, to see if it might reveal what apps were unexpectedly busy behind the scenes. It did not help.
In the end, he resorted to turning off the Cellular Data switch in the iPhone’s Settings app, turning it back on only when he intended to use the network. This obviously worked to avoid the charges, but was inconvenient. After a couple of weeks, he experimented with turning Cellular Data back on again as a default. The unexplained data usage did not recur. It had vanished as mysteriously as it had arrived. End of story. For now.
With the problem apparently resolved, and no clear way to figure out exactly what had caused it, I let the matter rest. Then, a week ago, a second friend emailed me with an almost identical issue. Figuring that where there’s this much smoke, there might be a fire, I searched Apple’s Support Communities. Sure enough, I found several threads citing complaints of this same symptom—most notably a massive 93 page thread titled “Unknown data usage early morning.” The thread first appeared in June 2010 with updates as recent as the last few days.
While I haven’t read every post in this thread, a scan of the thread revealed some interesting tidbits:
• While AT&T’s billing may cite the usage as occurring in the early morning hours, this is most likely not when the usage actually occurred. As AT&T explains:
“Many smartphones (including iPhones) are ‘always on’ data devices. They establish a data connection with our network and keep it open even if there is no data being transmitted. If the customer does not end their data session, it is recorded during a nightly feed to the billing system. The data session can contain billing for all the data that was transmitted throughout the day.”
The AT&T statement did not make clear exactly when this “always on” is in effect nor how to end a data session. As such, I remain skeptical of this explanation. However, yet another quote from AT&T makes a similar point:
“There is no such thing as ‘phantom data.’ The data usage on your bill reflects all the data you use during the time that your smartphone is connected to the network. AT&T captures your data activity nightly to create a bill record in our systems. This will appear on your bill to be a late night ‘charge,’ but in fact, the time stamp reflects the time that your device established a connection to the network, not the time that you sent or received data.”
• When your iPhone goes to sleep, its Wi-Fi connection is typically terminated but the 3G connection remains active. As such, if information is being transmitted over the Internet while the iPhone is asleep, it will go over 3G even if you have an active Wi-Fi network that the iPhone would otherwise use. [Note: My research indicates that this is true only if the iPhone is not plugged into a power source. The idea is to conserve battery power while the iPhone is asleep. Wi-Fi shutdown during sleep also does not apply to Wi-Fi-only iOS devices, such a the iPod touch, as they have no 3G alternative.]
• A “rogue” application may be generating unexpected 3G usage (as noted in a posting on this page of the thread).
• While AT&T may initially refuse to offer a refund for any mystery overcharging (as they did with my friend), persistence will likely pay off. Keep insisting that you deserve a credit and they will eventually relent. At least that’s what happened to many people posting in the Apple thread.
• There is a pending class-action suit regarding “phantom data” charges by AT&T. There now seems to be a related second suit. I’m not sure what the current status is of either of these suits. AT&T, of course, denies the charges.
In the end, no one seems to know for certain what’s behind most of these mystery data incidents. So I can’t offer any certain advice on how to avoid them. My strategy has been to hope it never happens to me. So far, that’s worked.