Apple has released detailed support information explaining the differences between iPhone calling features on the AT&T and Verizon networks. Because AT&T Mobility uses GSM technology and Verizon Wireless has a CDMA network, each iPhone 4 has different calling capabilities. Recently it was revealed that Verizon’s network suffers from conference calling limitations, but there are other differences as well. The table below was released by Apple to illustrate the details. more info