Unlocking my iphone

[DC55]

I need some help, I'm confused about a few things regarding unlocking an iPhone. First of all, if I go and buy an inactivated iPhone from eBay, can I jailbreak and unlock it and get free network services like data and not be stuck in a contract or have to pay monthly fees? Also, which carriers will I be able to use and what features might I lose depending on which carrier I pick? Right now I'm currently using sprint and I hate it, I constantly get overcharged for data even though I had the unlimited plan (which I ha to turn off) and no matter what phone I get I have issues with sending and receiving messages. Sometimes it takes me 30 minutes of continuously hitting resend on my phone to finally get the message to be sent and even if it says it faile the message will get sent like 10 times. So I'm looking for an upgrade and I have an iPod touch 4 and I love it, I just want a phone I can make calls on and text with using 3G that's as good as my iPod and it would be nice to be able to unlock an iPhone and use it on sprint service without having to pay ANYTHIG. Please help, I have visited various websites doing enormous amounts of research and I can't find what I'm looking for, can someone help me?

[i.Annie]

Well firstly depending on which iPhone you have to see what baseband it's on.

5.13.04 and below on iPhone 3G/3GS is unlockable. Anything above like 5.14.xx and 5.15.xx is not. Beware of any that is on 6.15.00, that's unlockable but GPS on those phones are broken. You cannot restore to stock firmwares on those devices either.

Also, if it is an iPhone 3G, you can restore to a stock firmware with that 6.15.00 baseband to 3.1.3 but like I said, GPS is going to be broken.

When you get an unlockable device, you can use it on any GSM network. You will not however be able to use 3G data speeds, only EDGE on any network that isn't AT&T. so say you want t-mobile, it will not be able to access 3G speeds.

[DC55]

What exactly is EDGE? sorry I'm new to this so I apologize if I ask alot of questions haha I just wanna make sure I have everything figured out the right way