Lost my iphone. Will the thief be able to access to my data?

My iPhone 4s (ios7) was locked when it was stolen, and the thief turned the phone off right after he stole it. I immediately activated Lost mode through Find My iPhone, but it seems like he took the sim card out. I believe that Find My iPhone is pretty much useless once the sim card is removed before the lost mode of Find my iPhone gets activated. My question is that when one takes a sim card out from an iphone, does that automatically unlocks the phone? Or would they be able to unlcok the phone without losing the data (assuming that he doesn't know my passcode)? My phone probably is already sold by now, but I'm just wondering if he/she would be able to access to my photos, notes, and etc.

thanks in advance!