I responded.
I would be seeking the cheapest option for adding a new line as I don't have a use for it other then trying to keep my unlimited. It isn't worth worrying about cancellation fees from VZW and another store. I'll just pay the $199 for the new phone. I know that I'm going to use more data then I've been using (currently, under 2gb/mo) and do not want to lose the unlimited. IMO, paying $500 or $600 for a new phone does not make sense. It may suit others.
The new line will pay for itself if you have 2 unlimited data lines that you can transfer their upgrades to the new line and use one of the transferred upgrades to buy an iPhone 5 and sell it on swappa.com. Here is how it works:
Get your GSIII by adding a line through VZW. That is $200 + the cost of the new line ($10/mo + taxes/surcharges = $15/mo where I am = $300 for 20 months) + $35 activation fee + tax on the phone. I don't know how much tax is on the phone where you live, but worst case scenario is CA where they charge the tax on the full retail value of the phone. Just to make this a round number, let's say that is $45. So price for the phone for 20 months (time until the next upgrade is available on the new line) is $200 + $300 + $35 +45 = $580.
Of course you have to activate a basic phone on the new line to get rid of the data plan for the price to be only $300 for 20 months.
Then when your upgrade comes up on your unlimited data line, you transfer it to the basic line and get a 16GB iPhone 5 for $200 + tax = about $250. Then activate the iPhone 5 on the basic line then activate a basic phone to remove the data plan, sell the iPhone 5 on swappa.com for $600 (which is what they are selling for now, but it may go down in the future) - minus the $10 swappa.com fee and $10 insured shipping cost = $580. There may be paypal fees, too, so you need to factor that in but I don't think they are huge fees.
So you end up putting out $580 for the GSIII, then $250 for the iPhone 5 but you can recoup $580 for the iPhone 5 by selling it on swappa.com so in the end, you got your GSIII for $200 + tax, which is the upgrade price, and were able to keep your unlimited data!
Then when your second unlimited data line's upgrade comes due, you transfer it to the basic line repeat the steps above for the iPhone 5 but instead of selling it, your other family member gets a new phone at the upgrade price while keeping unlimited data!
And when the new line's upgrade comes up in 20 months, you can get another iPhone and sell it to recoup the cost of the new line for another 20 months.
Now of course, if in the future VZW closes the loophole so that you lose unlimited data with the transferring of upgrades from an unlimited data line, then this won't work in the future. But for now, it works.