Hi djltoronto,
My apologise. I did not describe it properly.
When i am on the phone, and if i did not subscribe call waiting, the second and subsequent incoming calls (while i am on the line) may not able to get connected. My service provider do sent me a message informing me which number has called earlier. This is the one i am referring to. My old Sony K800i has this feature. It show right after my call and it only appeared at lock screen status.
Thanks.
that's much more complicated... but if you do not have call waiting on your account, and missed call while you are on a call can only be handled by the service provider (not the phone), since that call never reaches the phone.
Some service providers have network features which can send you a text message or some sort of notification of the missed call - but that feature has nothing to do with the iPhone. it's a network feature.
I am with Bell - and they do not have such a feature - my GF is with rogers, and they do have this feature (free) and they call it "who called". With rogers, it even works if your phone is off. When you turn your phone on, you will get notifications of who called while your phone was off (or calls missed while you were on the phone).
Hope that helps. - call your service provider.