This is a major flaw with CDMA based networks, which is why VoLTE couldn't come soon enough! Here is the issue: On AT&T, a call comes in while you're on another call, you can easily swap back and forth between calls, and hang up on another. You can accept as many calls as you want as the iPhone always keeps one "line" available. If you ignore the incoming call, the network automatically sends them to voicemail right away. The ability to hang up on one call and go back to the other is often overlooked, as well as the ability to switch back and forth between calls On AT&T, the phone also provides you with the option to End + Answer, which is a function I use, but many do not see the need for. On Verizon (and maybe Sprint, but I have only used Verizon), a call comes in on another call, you hear one tone. Your options are Answer, Answer + Merge, or End (both calls). You answer, but when you hang up, both calls hang up! This is a huge major flaw. THEORETICALLY, it is supposed to ring again, you pick up and then it connects you to the other person....This has never worked. Another flaw in CDMA is the adding calls ability. When I added a call on my VZW iPhone 4, it connected fine, but the ability to swap back and forth, for some reason was not available. The button was GREYED OUT! You had to hang up on the second call to go back to the first...and even then, it wouldn't even go back to the first, you just hung up on them both. To the client/customer/other party, it seems like you just hung up on them. Another issue would be in billing, because the other person hung up, the phone still seems to register it as both calls being connected on CDMA, thereby taking away double the minutes. Whereas on AT&T, the other call promptly disappears from the screen when they hang up, freeing that slot, as well as not counting for double the minutes. Other issues I have with the VZW iPhone: The counter on GSM iPhones (AT&T), will not start counting to 0:00-0:01 etc until the call has connected whereas on CDMA, it starts counting right away (does this mean I am being billed while its ringing, instead of when the call started?). If someone can shed some light on the situation, it'll help me better understand Verizon/Sprint iPhones better, and I can instruct people how to use their phone properly. I only have true real experience with the AT&T iPhone.