Have tried this on both the Edge and 3G networks and keep running into the same problems. Seems as when ever I am in my office building or my home my phone keeps dropping the call. I keep getting the call failed screen. I am running 5.1.1 with the new JB but this problem was happening before I recently updated as well. My friend went to the Apple store here with his stock iPhone 4s with the same problem. They gave him a new SIM card. I would rather not have to go through the hastle of restoring to new and going into the Apple store for just a new SIM card. Is it possible it is just a ATT network issue in the area or is a new SIM card the best fix for this issue?