Ultrasn0w tool was developed by iPhone Dev team with the contributing help of @sherif_hashim and @Oranav. This software unlock is the most popular among iPhone users from around the world.
Supported Baseband for Ultrasn0w 1.2.8
Go to Settings – General – About – Modem Firmware and compare digits with shown above. Don’t worry if you don’t see your baseband in a list. Because there is a cheap IMEI unlocking method. You can use it to free iPhone from AT&T or find solution for other US and international carriers and forever forget about worries regarding losing unlock during baseband and iOS update.
I know that it is not for free but you will get it permanently with official confirmation from service provider and Apple.
If everything is fine be ready to the next step which is very important for iOS 6.1.3 unlocking with ultrasn0w as well. Only jailbreak can help you to perform this.
You may know that there isn’t untethered jailbreak for iOS 6.1.3 but there is a tethered with two working tools:
You can always use comment section to ask questions and look for answers and error fixes however the process is easy and you can just turn on/off Airplane mode or reset network settings if you see No Service.