Ultrasn0w is the iPhone carrier unlock utility which can be installed and used via Cydia on Jailbroken iPhone.
Ultrasn0w can be installed from it’s original official repo: http://repo666.ultrasn0w.com/ . However, sometimes there can be error while trying to add that repository as source or while trying to install ultrasn0w from there. For these situations, here are the alternative repo for ultrasn0w download and installation to unlock your iPhone.
Ultrasn0w repo alternate sources for cydia
Following are the alternate repo for ultrasn0w (you can add more by mentioning them in comments):
Also, make sure that you enter “http://” while adding the source name!