From my Samsung Galaxy SIII's Phone application (on Android Jelly Bean 4.3), as long as my phone has credit, I can access the application's "Settings" screen via the menu key and then tap on "Additional settings" to check the "Call waiting (During a call, notify me of incoming calls)" feature. With this feature, when I am on the phone, if someone else calls me, then the speakerphone emits two beeps, followed by a pause, followed by two beeps, and at the same time displays a screen where I can answer the incoming call. The beeps are not audible by the party already taking part in the phone conversation. I then have the option of answering the new call, while putting the old call on hold, or reject the new call, optionally rejecting it by also sending a text message displaying the reason for the rejection (e.g. busy, etc...). In case the new call is answered, the other call is put on hold, and I can then either swap which party is on hold and which party is online via a button on the screen. I can even merge the two calls in which case I will be hearing both other parties at the same time and they will also be able to hear each other.
So, all in all, Call Waiting is a great feature because when someone calls you and you're busy on the phone, you still have a chance of at least answering the new incoming call if it is more important than the current call. However, this feature seems to be lacking on Android Gingerbread devices.
So, my question is, why is the Call Waiting feature missing from older Android devices? After all this feature has been available for a very long time on phone networks (including those times when there were no cell phones and this feature was available on landlines and was used mainly by people at work who made use of the feature at an additional cost)?