How to unlock my iphone for tmobile?

Ok so I recently got Iphone I ALWAYS wanted and had to get cause I lost my phone+simcard.

So I bought this Iphone off craigslist so it doesn't have a simcard that comes with it and I have no clue how to unlock it + it won't let me do anything without a simcard.

I have a brand new tmobile simcard sitting right next to me though, how do I unlock this phone!

You can Factory Unlock it online to use with your T-Mobile Sim card.

You can get any AT&T iphone unlocked here: http://gsmunlocklabs.com/unlock-iphone/

all you need is your IMEI and iTunes. It couldn't be easier.

After we unlock your iphone connect to itunes with a non accepted sim (for example a tmobile sim) and do a back up and restore. Your phone can now be used with any gsm network. You can safely update the OS on your handset at any time, and sync your device with your computer without fear of Apple removing your unlock
We provide an AT&T Official, Permanent, Apple unlock that remove any network restrictions your iPhone may have by marking your handset as unlocked in Apple's IMEI database.
Once your Unlock has been processed just follow these simple steps:

1) Open iTunes on your Mac or PC (verify you have internet connectivity).

2) Connect your iPhone to your computer using the USB data cable.

3) Backup and Restore your iPhone using iTunes.

4) Once your iPhone is restored it will have the Factory Unlock in place!

http://attiphoneunlocker.com/