Beside the lack of video calling & the lag time for any function accessed when in a call,

First it's difficult to switch between calls or resume a previous call after hanging up with a call on hold. You should not have to enter the menu to change between anything. That submenu should be available automatically when a call is placed. There is a gigantic space where a tiny little thumbnail fills barely a third of the open area (which looks so outdated in comparison to the iPhone). This space could actually serve a function!
Logic-When someone's waiting on the other line it is simply not convenient to have to click more than once to get back to them or switch between parties.
Second when you click on one of the phone numbers appearing in your call log it should dial that phone number immediately! If you click on the contact's image it should give you the submenu to choose between different phone numbers, sms, mms, or IMs. It should not take multiple taps to call someone back-that is simply not convenient either.