There are a few issues that I understand when trying to do this (from reading about it online since the release of the device)...
1.) The IMEI is not recognized from Verizon since it is not registered with their network, so essentially, they won't help you do anything related to the device since it is not officially "their own".
2.) The MEID is not registered with Verizon, so while LTE will work across the spectrum (except Sprint), CDMA will not unless the phone is officially registered.
3.) The SIM used must be a SIM that is FROM another registered iPhone (5S or newer nano-SIM) and must be a registered account in good standing, otherwise it won't work at all. You can't take a nano-SIM from another device and use it from what I understand, it must be from an iPhone user.
...all that said, lots of people have made it work (most of them reporting a handful of issues from data problems to no visual voicemail and other little quirks)...honestly, I think I would just sell that model and BUY a verizon specific one and skip the whole ordeal.