According to CNET, Verizon Wireless will begin SIM-locking its smartphones out of the box at some point this spring. Essentially no details are provided about how this will be implemented, but it really doesn't matter, because Verizon rather explicitly agreed not to do this ten years ago.
Per the restrictions imposed by the 700MHz Upper Block C spectrum auction it won in 2008, Verizon is expressly barred from locking down handsets on its network that utilize this spectrum. The plain text from the restrictions makes this absolutely clear.
(e)Handset locking prohibited. No licensee may disable features on handsets it provides to customers, to the extent such features are compliant with the licensee's standards pursuant to paragraph (b)of this section, nor configure handsets it provides to prohibit use of such handsets on other providers' networks.