Why don't I see a call waiting notification on outgoing calls when other person is on another call?

I have been using iPhones for nearly 6 years now. One thing the iPhone does not do that my Nokia phone does is tell me when someone I am calling is on the other call. The Nokia would say "Call Waiting" on the screen so I would know why they could not answer. Please don't tell me that this is a carrier feature as I am using the same carrier on my other number with Nokia phone. And also please don't ask me why I want this feature because it's irrelevant. Just want to know if iPhone has this feature or not. And if can be turned on somehow.