I believe you can buy a phone elsewhere and maintain your plan too. It's the contract renewal that happens when you get a subsidized phone that will remove your unlimited data.

I don't remember the source on this but I believe that will only be true for 3G access plans. To use it with a 4G device, you'll need to upgrade your data plan and that means that you'll need to agree to the new terms.

That's not true. I have a 4G phone and was able to keep my existing, unlimited plan for the same price.

You can buy one at full retail price through Verizon and keep unlimited, but there's no point in that when you could buy used off eBay/Craigslist and save relative to the $650 off-contract price.

Well, the point for me was less screwing around. My phone was dying while traveling, so I went into the nearest store. They in effect offered me a $400 subsidy if I signed a new 2-year deal and gave up unlimited data. I was happy to pay the full price to avoid that and still walk out with a new phone.