Jazman is partially incorrect. As stated, you cannot use a GSM (8220) on the CDMA network. You'll need an 8230. But you cannot put a non-Verizon device on their network, they will not allow it. No amount of unlocking (even if a CDMA device can be unlocked) will make it happen.
The 8230 is no longer sold by the carriers, but you may find a used one, but before you buy one read this (it is applicable for any used BB purchase) Buying a BlackBerry off eBay - BlackBerryFAQ