GEVEY Ultra S for GSM iPhone 4S for iOS 5.1-6.1.2 (unlock your iphone 4S)
It's open, I've used it for 1 week but got a Nexus 4 so no need for the Gevey anymore.
It works for iOS 5.1-6.1.2, supports Modem Firmware or baseband 1.0.14, 2.0.10, 2.0.12 and 3.0.04
I have it running on iOS 5.1.1, MMS, imessage and facetime works like a charm.
More info here: http://www.gevey.com/gevey-ultra-s-for-gsm-iphone-4s/
Location: Markham, Richmond Hill, Humber college north campus, York University keele campus