AT&T and Apple are working on a software-oriented remedy for the problem, which some analysts believe originates with German-made Infineon "chipsets" that allow the iPhone 3G to move from one network to another.
Switching networks should be "seamless" USA Today reported.
Roger Entner, senior vice president at Nielsen IAG, said the problem exists "in every market where the iPhone 3G is sold."
That points to a problem with the phone, rather than with the AT&T network, Entner said. Senior wireless chip analyst Francis Sideco told USA Today the problem could be "as simple as a solder joint."
The worst case scenario, analysts say, is a recall of the phone that has sold so fast since it was launched on July 11 that stores have trouble keeping them in stock.
A recall would an expensive and embarrassing set back for the company, analysts said.