I'm curious as to whether you live in a large city/town, or if you're more in a country-side area. If what was said above was true, about the cellular towers, it may just be that the towers you used to use are no longer available because of the merge. I wouldn't think that in a highly populated area there would be much of a change because of the modicum of cell towers available to use. As said before, I would contact Cingular/AT&T and ask them if other people in your area have called about the same problem, and how they went about rectifying it.