IPhone 3GS carrier switching

I recently got an iPhone 3GS from my cousin for free, but its locked to AT&T. I want to switch my carrier to tmobile somehow, because I have a SIM card that is fully working with my Samsung phone. Is there anyway I could change my carrier to tmobile? Thanks!

Added (1). EDIT: I want my iPhone 3GS to work with tmobile I meant

IPhone5 or Samsung galaxy S4?

I currently have the iPhone5 and I just feel so let down by it due to messages taking hours to come through and messages disappearing when you unlock the iPhone. Anyway I enjoy how simply the iPhone is to use and OS on it and how simply the app store is. I have watched a number of videos and still not sure which one to get? As my current contract runs out Wednesday.
Also can use S4 on iMac? And can you convert iTunes music onto S4?

Any help?

How much should in sell This iPhone for?

Right, I have an iPhone 4 16GB Black Unlocked

It has a perfect screen 0% scratches as I used a screen protector from day 1.
Operating perfectly, touch responsive, perfect battery etc.
The Wi-Fi is poor range
And the SIM card reader won't recognise sims, the reader will have to be replaced and I'm including a new sim reader with this. These are the only two problems.

PRICE IN € Please.

Stuck in DFU mode iPhone 4s?

My phone is stuck in DFU mode. I have tried plugging it into my computer, but it won't recognize my phone, I've tried different computers, different cords, and different usb ports. I've tried the 'hold the buttons for 10 seconds, and then let the home button go' trick, no luck. I'm really frustrated as no one has been of any use. I've tried everything I know of. I don't care if I upgrade my phone to iOs 6, or any of that, I can deal with it. I can re-jailbreak my phone, and get all of my contacts again if I'm forced to reset it. I just want to be able to use my phone.

Added (1). I have iOs 5.1.1
iPhone 4S

How to fix this computer problem?

I have a DELL desktop This is what happened:

I was playing fine on my computer. It was working and everything. I leave the house to do some errands. I leave the computer open and the monitor off because I thought that I would be back very soon. However, there were some things that happened which resulted me coming home later than I expected(around 3-4 hours).

When I arrived home, I expected my computer to be still on so all I had to do was turn on the monitor. When I turned it on, I discovered that the computer had shut itself down. I started the computer up again, however, it didn't start up normally. As it was starting up, there were some internal computer engine noises. I got scared and thought it was going to explode.So, I force shut it down by holding the power button. This time, it started up perfectly, however as it got to the Windows XP loading screen, it suddenly turned to a screen that said something about a floppy diskette seek failure. I didn't know what to do. So I searched for how to fix it on my iphone. I found the solution. It told me to go to boot menu and remove the USB Floppy Drive from the Boot Sequence and turn the diskette drive off from the "Drives" category. In the solution video that I watched, it worked perfectly, but on my desktop, it totally failed. The floppy diskette seek failure disappeared, but another problem occurred.

It was starting up perfectly until it came to the screen where it said, "We apologize for the inconvience, but Windows did not start successfully… Blah blah." I chose "Start Windows Normally" option. It did nothing and came back to the same exact screen. This happened two days ago, I thought it would be fixed if I left it alone for a few days. I was very wrong. The same problem is happening. I turned on the computer today, hoping it would be fixed, it is still looping as I'm typing this.

So, Please Help ME! Thanks IN ADVANCE. WHOEVER FIXES THIS IS A REAL LIFESAVER!

Can I get my Iphone screen fixed at the mall?

I was wondering if I could get my front phone screen replaced at those kiosks in the mall that people go to so that they can have colored phone backs? I know that apple won't help your phone or do anything for you if you go to them but I don't have AppleCare and it's absolutely ridiculous to pay a $169 deductible on a phone that I got for free with a 2 year contract.oh by the way I have Verizon. So if someone could answer my question without being a smartass, that would be fantastic.

How much for two iphone 5 from at&t?

Ok so i know the 16 gb is 199 for a two year contract.
Now monthly for unlimited everything, how much would both phone be in a family plan.
Plus i looked it up on their site and you gota pay data separate. I know if you go to the store in person its not like that, the data will be included with the unlimited everything… Or so i think. Lol help

My jailbroke iphone won't sync with itunes after update 6.1.3?

My iphone won't sync with itunes on the computer i had removed everything from my iphone and made it out like a new iphone now i can't sync to itunes meaning i can't use my phone

Added (1). It was syncing before it just happened as soon as i wiped my phone and updated it