You may start with a crisp, uninterrupted conversation in one location and simply moving several feet in another direction causes your phone to drop cellular signal. Unfortunately, AT&T is no exception to having bad reception depending on your location. There are few remedies that can assist with increasing the cellular signal of your phone, particularly in your home.
Visit AT&T's website and click "Coverage Map" at the top of the page to determine the coverage strength in your area. If there is little to no coverage in your specific location there is little you can do to increase the signal. Knowing your coverage signal will save you time from trying to figure out why your phone has low reception.
Position yourself in various areas to see if you experience a stronger signal. For example, you may experience stronger reception if you move closer to a window.
Purchase a Microcel 3G from AT&T. The Microcell is like a mini cellular tower that connects to your current broadband modem. It boosts the signal range in your home which will increase the bars on your AT&T phone. Contact customer sales or visit an AT&T store for pricing. There are other "mini towers" you can purchase that may increase cellular signal but ensure you read the label to verify it will work with AT&T service. You will connect an Ethernet cord directly from your modem to the Microcell and plug the Microcell in the nearest wall outlet.