If the latest version 3.0, including the baseband upgrade, is upgraded to the iPhone, then they are not alone. Although Apple and AT & T have improved their services, rejected calls are still real.
The following steps can help you reduce missed calls
1) Use the Field Test mode on the iPhone to determine the signal reception levels: the command # 3001 # 12345 # * and press the Call key. This displays the Field Test main menu. Note that the signal strength bars in the upper left corner of the screen should be replaced with the signal strength in decibels. The signal strength appears as a negative number and the smaller the number, the better. For example, -75 is better than -99. The signal strength between 60 and 80 can be considered good reception.
Use this feature to determine where the best reception is located. If you have problems with missed calls, you may prefer these locations.
2) Turn off 3G to improve your phone's performance: Turning off 3G in an emergency in an emergency will always help you get better. For the better, 3G has been turned off for the most part of the time, and you can only turn it on if you want to browse the Internet or download the app from the iTunes App Store.
3) Using Wired Headphones: Using a wired headset can improve signal strength as the cable from the headset also works as an extension for the internal antenna.
4) Hold the iPhone on top: The iPhone antennas are located at the bottom of the device. If you walk around the phone at the bottom of the phone, it slightly reduces the signal. A device near or on the iPhone can cause a large difference in low signal strength.