And we're out of the sandbox with @saurik's invaluable help! (well, at least there's a PoC) :D Turning out more complex than X-Gold 618.
The X-Gold 618 is the baseband platform used in the iPhone 4 and iPad 2 (GSM). The Qualcomm MDM6610 is the baseband chip used in the iPhone 4S, for those wondering. As planetbeing notes, more work was needed to escape sandbox for this jailbreak than was needed to escape the iPhone 4 baseband's equivalent of a "sandbox".