If I buy an unlocked iphone 3, 4, or 5 can I just put my sim card in it?

I have a Motorola Atrix 3G and the 2GB data plan on AT&T. Can I buy an iphone 3, 4, or 5 off of the internet that is unlocked and simply put my sim card in it? As I said above, I already have the data plan. So will that automatically just work in the iphone? Do I need to get a new contract or something? Will AT&T bill me for something simply because I bought the iphone from an outside source and just stuck my sim card in there? I have no idea if this is illegal or not to do so can someone also answer that for me please? Sorry for all the questions haha, and thank you in advance!

Iphone 4s Jailbroken update?

We have tmobile so my dad bought an iPhone 4s and got it jailbroken. So today he updates it and now we're scared that his phone may not work. Right now it says that it needs to be connected to itunes but I'm not home and my computer is broken.

Are iPhones for people or families with a lot of money?

I hear this a lot, "oh you have an iPhone you must be rich." Its true my parents make well over 150k year and all 5 of us have iPhones and I live in a wealthy town where nearly everyone has an iPhone but they aren't that much $ especially since you could get an iPhone 4 for FREE. So why do people have these preconceived notions that iPhones are reserved for the rich?

How to switch from imessage to textmessage? (iphone)?

I just wanted to ask how to send an iMessage as a text message.
whenever i want to message my dad it sends it as imessage automatically.
but sometimes he doesn't get mine (i don't know why but this is not relevant) so i wanted to know how to send it as a text message to him? I get his messages as text message but i can't seem to text him back!
I tried everything.

Can you fit an iPod 4g into an iPhone 4S case?

Okay we'll, you guys are probably say no, but I saw a YouTube video of a girl with an iPod and she put it in an iPhone case easily and I just want to know for sure because my phones not due for an upgrade for more than a year but I really want an iPhone and with my iPod I want my friends to think I have an iPhone.

WTF WHY DID SHE IGNORE ME WHEN I SAID HI?

Katie's supposedly a popular girl.everyone knows her. I sometimes go to her church. She's best friends with my cousin, and we all sit together at lunch with a 2 more girls and they're all best friends. I was walking to class and i say "Hi, katie" and she walks by me not saying anything. I thought she misheard so a week later I say hi again. She looks at me and just keeps walking!

I'm OUTRAGED! SHE COMES OVER TO HER LITTLE COUSINS HHOUSE NEXT TO MINE AND ONCE SHE STAYED OUTSIDE AND WE TALKED ABOUT OURSELVES SHE WAS So NICE AND I TOLD HER SOME PERSONAL STUFF TOO. THEN THE NEXT TIME SHE COMES OVER TO THE COUSINS HOUSE WITH HER MOM SHE STAYS IN THE CAR WITH HER SISTER ONHER IPHONE AND SHE CAN SEE WE'RE OUTSIDE BUT IGNORES US EVEN WHEN WE WALKED BY THE CAR (I DIDN't SAY HI THO). I BET SHE THINKS I'm A KIND OF WEIRDO CUZ WHEN THE NEW YEAR STARTED MY COUSIN STARTED IGNORING ME SOMETIMES TOO (ME AND MY COUSIN DON't HANG OUT. CUZ MY PARENTS.)

Added (1). New school year started*
The only thing personal i said was how my parents were super overprotective about clothes and hanging out with people

Added (2). My question is why did she rudely ignore me and is rude with me

Why does everybody in love with iphones?

Android has improved drastically and is now way ahead of iPhone. You can buy a galaxy s3 or a galaxy note for the same price as a little iphone 5… Why are consumers so dumb? Iphones are OK but way overpriced and there's no way to customize them without jailbreaking.

Added (1). *why is everybody in love with iphones?