I'm using an Iphone 4 with the Microcell and have had audio out problems. I've read postings about turning off the Cellular Data, yet an ATT tech mgr has told me that it has NO effect on audio in or out. But doesn't use bandwidth? What is the experience of the Community?
If you sound choppy to other folks you call while using the microcell, then your problem is that your internet connection's uplink bandwidth is saturated and packets from the Microcell are being dropped.
The only fix is to either use the so-called "priority mode" installation or set up some sort of QoS configuration in your router.