I pre-ordered my VZW iPhone 5 from Best Buy. It was in stock and I picked it up this morning. I have the UDP, my mom has a basic phone and an upgrade. I had the nice sales associate upgrade her to the iPhone 5. The nice sales associate put my mom's basic phone back on to her line. The iPhone 5 is off this whole time. When it came time to put the iPhone 5 on my phone number, VZW kicked it out saying the SIM was already associated with another number (mom's).
I went to the nearby VZW store to request a new SIM. They had plenty in stock but I was told by two different people (one a manager) that she could not give me a SIM card knowing that it was going to be put into a discounted iPhone 5 in order to keep the UDP. I explained to her everything discussed in this thread as well as my previous convo with VZW's phone support that it would be possible.
I went to another VZW store near my law school and was told that it IS possible to do the aforementioned procedure but they were all out of SIM cards. I had this nice VZW sales associate call the local store I was just at to have them hold a SIM for me. When I showed up, I went to a different associate, said a SIM was waiting for me. After a few clicks of the mouse, a SIM swap, and a pleasant wait for activation, I now have a fully functioning iPhone 5 on Verizon with unlimited data.
For what it's worth, having an iCould backup of my old phone in the cloud was awesome! Once on wifi, I did a complete restore and it was like I had never switched devices.