I have had the same problem since I got the iPhone 5 in September 2012. Since then, I have had 5 phone replacements, 4 SIM card replacements, closed my AT&T account and reopened it, and tried a new phone number. None of these has fixed the problem described in this forum. I am in Cincinnati, Ohio. SIM card replacements will give you a few days of being able to use data and voice at the same time at 4G speeds. Then the problem returns. Like others have said, if you toggle LTE off in settings, you get a day or two of usability also.

It sounds like this is a bigger issue. Has anyone come up with a solution? As you can tell, I feel like I have tried everything possible to fix this. Many of the AT&T support people I have worked with have been great and have wanted to help me, but so far, no solution has been found.

Any help would be appreciated!

Thanks,
Jason