Is it legal to unlock an iPhone without getting to actual company to do it?

I'm just really curious because now that the iPhone 5 is out, iPhone 4S is much cheaper, and iPhone 4 is free on AT&T. I have T-Mobile so I feel really left out. I have an Android, Motorola Defy, but it just doesn't seem as great as when I had an iPod Touch, so clearly iPhone would be even better than that! I've been looking online and noticed on some sites like Craigslist that people unlock iPhones for really cheap. I was wondering if this could be my answer for a T-Mobile iPhone, but I don't know if it's legal to do since Apple didn't approve of it being unlocked for me. So if I did get it unlocked, but then something bad happens and I need to send it back, would I get in trouble! Can someone please help?!~

Can I delete the duplicate photo albums from my iPhone?

My phone has the first 700 pictures from my phone duplicated twice on my iPhone 4.Is there any way that I can go in and delete the two extra albums? Either from my phone or my computer? And I've tried to delete pictures just like I do in my camera roll, but it doesn't have an option to delete that I see. Help please! It's taking up a TON of my memory

Risks about updating software to iOS 6?

I have an iPhone 4 with 32 GB and have pereviously updated to a newer software before. Anyway, what are the risks about downloading the software? The positives?

Does iPhone 4 have siri on ios 6?

I'm going to buy a iPhone 4 but I'm wondering if it has siri on the new update ios 6 on the iPhone 4. DON'T ANSWER THIS IF YOU DON'T KNOW! And don't say just buy a iPhone 4S there 99.99 right now. I'm buying it off Craigslist so shut up

What does unlocking the iPhone do? Will I get in trouble for it?

I currently have an iPhone that is under AT&T. I want to stay with AT&T. I don't want to move to T-mobile, Sprint, Verizon, or anything else. I want to unlock it, just in case I'd want to use it overseas with another SIM card. If I were to unlock it on my own, would AT&T charge me anything? Would I automatically be kicked out of my contract and be forced to pay a termination fee of any sort? I don't plan on manually calling AT&T to end the contract, because I still want to stay with AT&T.