With the unexpected release of the evasi0n7 jailbreak, we are finally able to release the 3GS/A4 6.1.3 + 6.1.5 untether Cydia package.
To get the package you must have already performed a tethered jailbreak via redsn0w or sn0wbreeze. Simply open Cydia, refresh the packages from the Changes tab, and then search for “p0sixspwn”.
Sn0wbreeze will be updated at some point to incorporate the untether directly. The next priority is a jailbreak for all devices on iOS 6.1.3 and iOS 6.1.4, including A5 devices (iPad 2/3/4, iPhone 4S/5, etc).
H8sn0w says no eta, however:
We expect it should be out by Christmas day. So if you don’t feel like upgrading to iOS 7 and prefer 6.1.3/6.1.4, sit tight for a bit.