Call AT&T tech support and have them look it up for you. There is a known problem with iPhone's running iOS version 5.0.1 or higher and the Microcell. This has been known since last Novemeber 17th when the ticket was originally created. Don't let them tell you that it doesn't exist. It does. I have the information from at least two different tech reps. There is no resolution date as of a few days ago. I call them every other day just to annoy them and hope that one day it will be resolved. The symptoms that I am having is that the Microcell will drop my iPhone 4 (running iOS 5.1) suddenly and show "Searching..." or when I send and receive text messages rapidly (long or short, SMS or MMS) the Microcell will drop my phone and show either "No Service" or "Searching...". Most times it will pick up the Microcell again or if you put it into Airplane Mode for about 10 seconds and then out it will come back on. Worst case is to power cycle the iPhone. This almost always does the trick but is a real time waster and you never know when you'll lose the signal again. Today I went into my Microcell settings and changed the handoff to disable. I'm hoping that might help some. I'll report back if so.
Another problem that you may or may not notice is that when you are connected to the Microcell your battery life will drop considerably. Mine has. I work at home and I'm lucky if I have 5% by the end of the day unless I plug it in where I used to end the day with at least 50% to 55%. AT&T will not recognize this problem.
I hope this helps you.
