It has nothing to do with a phone and all to do with CDMA, and it is a major reason why I don't use CDMA. On GSM, I can make a 7-way conference call, take any arbitrary person and talk to them privately then join them back into the call or drop them.
If somebody is on call waiting, I have the option of talking to them individually or creating a new conference... This is exactly the case when we're in a conference and somebody's phone drops the call. I don't have to call the person I'm already connected to over again, which gets old quick.
My phone knows which calls were completed, and the exact time when answer supervision was detected. The phone log knows which calls I hung up on, and which numbers had a busy signal.
GSM can retreive and show you all of your call forwarding settings. Every feature code is standardized, including 911, and the IDD code, across every single carrier in the world. T-Mobile's USSD feature shows you your minutes immediately, without waiting for a SMS. Cingular uses the same thing to let you recharge a prepaid phone just by entering the card number.
This is all on my 8700, which supports almost every GSM call handling feature there is (I don't remember if it indicates when the other party puts you on hold), which not coincidentally, is what you get on an ISDN (or T1) PRI. On CDMA, they're, well, what you get on an analog line.