1) I don't think there is any 'easy' way to quickly enter SMS compose mode. It does seem rather silly that the default is compose email even when you are in the SMS screen.
2) While viewing messages, if you press Alt-P it will show you all of your calls. You can then highlight one of the date bars and press the menu/BB key and select 'Mark Prior Opened'. Press Back key to return to normal message viewing. BTW: Alt-S shows SMS messages and Alt-V shows voice mail messages.