Apple has posted a chart that shows how phone features behave differently based on whether you are using a GSM or CDMA network.
iPhone supports many phone features, including call waiting, call forwarding, and conference calls. Depending on your wireless carrier's network technology (GSM or CDMA), there are different methods for enabling and using these features.
wow just more reason not to change to verizon it sucks you need to remember all this codes instead of just going to you phone setting , also you can only make call with 2 person what a conference call i can make only with 2 people at lease att has up to 5