According to the Verizon people I have talked to, you do not need to transfer the lines en mass; you can do an AoL for individual or multiple lines. The phone number is tricky but there are ways to deal with it; especially if you are moving to a new carrier. That's what I will be doing. Long story short though, you will lose whatever phone number is associated with that account when you sell it.
Root: ask not why, ask why not.