You're ignoring all other expenses of attaining and selling these phones. If you discount their time and money spent driving all over the place to get these, the costs and time spent to reprogram or disassemble these, and the time and cost to market and sell them, you're a horrible businessman.
You're also ignoring the fact that these are commonly available in small quantity. Why buy 1000 of them and have that much money tied up if it's going to take you two years to sell them? Why risk that someone else will flood the market and the price you can get for them will plummet? Why risk that the service providers might change something to make the way you reprogram them useless?
It makes no sense to buy that many unless you can move them quickly for this kind of product.
A friend buys 1,000 tv antennas at a time from China and gets a terrific discount. He sells them on Ebay, 1 or 2 a day and gets triple what he pays.
Buying in quantity to get a discount makes sense. He gets them inexpensively because he buys a large quantity at once. There's no quantity discount on these phones. However, it he's only selling one or two a day, it's going to take him 2 or 3 years to sell them all. He's going to have to store hundreds of them for a long time. He's going to have to package them up and ship them individually.
His labor for putting them up on ebay, storage for all those antennas, taxes on inventory (if he runs his business legally), make that sound like a horrible investment unless he sells considerably more than 1 or 2 a day.
Another person buys left over summer clothes on the clearance rack at the gap etc.. she waits till next spring and sells them for 100% markup.
If you choose wisely, I'm sure you can make a bit of money doing this, however you're gambling that you know better than the professional buyers at the Gap, and that the sizes and styles that didn't sell (that's why they are on clearance) are going to sell next spring well enough to justify storing them, and the time and whatever other expenses are expended trying to sell them in the spring. Any that don't sell are a loss.
It doesn't take much before after the money you spend and the time you spend, plus the fact that you are either paying storage expenses or taking up a lot of space in your home you are paying for, you end up making very little money for your time, or even losing money.
But once again with buying these clothes, there is a reason why you need to buy them all right then. They are on clearance. With these phones, they can buy a smaller quantity and restock as they need more to meet demand. Why tie up all their cash on inventory if they don't need to do so?
This has devolved into an ebay seminar.
A few years ago, I met a man who deals in batteries for cameras. He employs 15 people in his shop and sells the batteries on ebay.
He goes to China once a year with a shopping list in hand and buys them by the container load.
He was one of a few people in an real ebay seminar that raised his hand when asked "which of you net $100,000 a year or more."
By the way, there are over 500 people in the U.S. that make over $1,000,000 a year net. Another statistic, there are over 15,000,000 items sold on ebay every week.
I never made over $200 a month in the years I did ebay, but then again, I didn't work at it. It always was a hobby.