What can thieves do with a stolen iPhone 4?

My iPhone 4 was stolen a few days ago.

It has a passcode on it, and the people at Verizon told me that they won't be able to get passed the first screen, but I don't believe that.

Everyone (in their right mind) has a passcode on their phone, and I've seen tons of kids at school selling stolen iPhones that have been reset and (somehow) unlocked…

what I want to know is, how did the person who stole my phone get into it, even though i have a passcode, and the find my phone app locked the phone?

since this is a major vulnerability, why hasn't Apple, or any other cell phone producer done anything about it?

I just have so many questions about this being possible… So if you've ever stolen a phone and gotten into it can you please tell me how thats possible
(don't give too many details because I don't want other people copy catting and stealing phones)

but I just can't see how that whole thing is done?

I can send text messages from my iPhone but can't receive messages?

I have an iPhone 5, and i was texting my friends (who also have iPhones) and my messages send to them as text messages (not iMessages) but their texts don't come through to me. I have a macbook air and have my phone number hooked up to messages, so i can receive the messages there, but not my actual phone.

How often do you shop at liquidation outlets?

I always shop there. There's a local outlet here that sells popular video games for $6. I bought Forza Horizon and Halo which is around $49 brand new and I've been playing them for months without issues. They also sell cool stuff there like iPhone controlled toys and w/e. Stuff that i didn't see at walmart or other huge retailers.

What happens when an officer says i will get a citation but he never gives me one. What do i do?

My friend found an iPhone and told me to hold it for him, the same day the officers at my school where looking through the picture on the phone and called everyone the saw to the office, and i had the phone so i willingly took the blame for it, the officer said i would get a citation for it but i haven't gotten anything. It happened on Halloween 2013. What will happen? Will it go on my permanent record? Will it be hard for me to get a job? I'm a High School student.