I constantly send messages to the wrong people with the iPhone...

You are right, it always defaults to the last conversation.

My worst screw up so far was this:

I send text messages to my alarm system to monitor the status of arm/disarm & to see when my wife leaves after I do, that she sets the alarm.

To do this, you need to send the message with your pin number to access your account, and I accicdentally send the message to a family member, and luckily, the response I got back was "what the ***k was that?"...

I merely responded by saying I must have pressed random buttons when trying to holster the phone while driving, sorry!

It is very annoying & I wish there was a way to have it default to home text screen each time... Now I am more careful.