A few hardware unlock solutions for the iPhone 4S have appeared this month, but Gevey has released a Verizon and Sprint unlocking solution. The Gevey Ultra S claims to unlock both GSM and CDMA, unlike the R-SIM and TP-SIM which do not work with Sprint models.
The new SIM interposer requires that your iPhone be jailbroken, not be running iOS 5.1 or higher and is on one of the following basebands: 1.0.11, 1.0.13, 1.0.14. This is also the only known solution for Sprint handsets. The Gevey Ultra S is $60 and will be available at the end of this month.
Online retailers like Applenberry are accepting pre-orders, but remember, these products can be dodgy so order at your own risk.