Even when you lock to portrait the phone still needs to do a transition animation.
Is there a way to completely kill all turning animation or at least animation related to the phone app and just have phone app pop in portrait? That quarter second or less turning animation can get pretty bogged when you already have a few apps open and running. I often miss calls if I don't have a bluetooth headset in where I can just hit a hardware answer button.
Turning animation is pretty in funtime apps but it steals resources for sparkle at the exact time that you really need all resources available to just take the call.