Here's the latest 'advice' from AT&T (note that at least 2 of them suggest turning off celular data... a process that is remarkably annoying and frankly makes the phone useless)
Dear XXXX User (name redacted)
If this is an OS issue- we would recommend that you go back to Apple directly to address those concerns as we have not had any communication from Apple that there is an issue with it.
Unfortunately, without seeing your phone and being with you when you use it we cannot duplicate the problem.
Here are some additional troubleshooting tips that I recommend you try this weekend:
iOS 6: Setup to Optimize Cellular Data Usage…
Many of the iPhone 5 iOS default network Settings are intended to create best user experience and performance, by utilizing available WiFi and high speed LTE and/or 4G Cellular Data networks.
If your cellular data plan is limited, less than a One GB per month, it would be wise to work through the defaults, and turn off those services that are not important to you.
Network Reset: reset the network connection…
Make sure you know [or have saved] your various wifi passwords so you can quickly set them up again.
Settings, General, Reset, Reset Network Settings.
Cellular Data: turn it Off when you don't need it…
This may sound messy, but it is really no more so than turning off WiFi, or Bluetooth, when you know you will not be using it. Maybe Apple will move this setting to the front page of Settings, as they have done with Bluetooth in iOS 6
Settings, General, Cellular, Cellular Data, Off.
iCloud Backup: Turn it Off except when you need to do a Backup to iCloud…
Otherwise iPhone will automatically do a Backup over WiFi and/or Cellular Network, while it is on Power, and sleeping.
Settings, iCloud, Storage and Backup, iCloud Backup, Off.
iCloud Documents & Data: turn off the use of the Cellular Data connection, until you need it…
Settings, iCloud, Documents & Data, Use Cellular Data, Off.
Location Services: make sure only the apps you consider critical are switched on…
These are new Settings in iOS 6.
Settings, Privacy, Location Services, and turn Off each Application that is not important to you.
Obviously you would tend to leave On Maps, Photo, Find Friends, Find My iPhone, Weather and Siri.
System Services: apparently, some of these can be demanding on Cellular Network usage...
Settings, Privacy, Location Services, and scroll down past the notes at the bottom of the list of Applications, and select System Services, and turn them all Off except Cell Network Search.
If the Maps Traffic service is important to you, turn it On, but be warned it may be a bit of a hog.
Notification Centre: work through each Application carefully, to determine what you really do need real time?
Settings, Notifications, select each Application, and turn Notification Centre, Off, if you do not need Notification in real time…
Siri: every iPhone User now understand how to use Siri…
However you should be aware that Siri support has been expanded significantly in iOS 6, to include operation of your iPhone, to send text, make appointments, find restaurants, make bookings, and handle your dictation. The catch is that Siri services contacts the Apple Server via the network to translate your voice, do the searches, and return your results. You can leave Siri On but be aware of using Siri, when you are only connected via Cellular Data, and low on Data Usage remaining…
Settings, General, Siri, Siri, On. by default,...
There is also a new setting included in several Applications which allow you to turn off the Cellular Data Connection while they are active...
Music: Settings, Music, Use Cellular Data, Off.
iTunes and App Store: Settings, iTunes and App Store, Use Cellular Data, Off.
Podcasts: Settings, Podcasts, Auto-Downloads, Use Cellular Data, Off.
Mail: you can set up mail to better manage Cellular Data Usage, if it suits your operation…
Settings, Mail, Contacts, Calendars, Fetch New Data, Push, Off, and set Fetch to Manually.
And select, Advanced, and for each Mail Account, Select Schedule, Manually.
And finally, here are a few more services you can probably do without, to further reduce Cellular Data usage…
Advertising: Settings, General, About, scroll down to Advertising, Limit Ad Tracking, On.
Diagnostics and Usage: Settings, General, About, scroll down to Diagnostics & Usage, Don't Send, On.
Some more tips…
For heavy data transmissions sessions on WiFi, switch to Airplane Mode, then switch WiFi back on again while your session is in progress. This mode will prevent iOS 6 from switching the Cellular Data midway through the session, should WiFi stumble….
Please let me know when you have had time to review by early next week so that we can proceed as I will have to put you back on the family talk plan and regular data plan next week and adjust the billing appropriately.
Thanks,
AT&T Rep