Beware:
If you drop money into your CC before spending, you can spend as much as you want.
More importantly: As soon as the iphone is rolling, prices will drop on eBay (and I mean drop), so you risk getting screwed big time.
Remember, lots of ebay sellers, are ready to earn a couple of $ per transaction, others got a free iphone as a present, and want to sell, etc, so those people would beat your price any time.
Don't want to sound pessimistic, but in my eBay powerseller days I've pulled of such shticks, but I only sold totally refundable phones (refundable for me), and I realized how badly I could have messed this up.
What's more: say iphones on eBay go between $900 and $700, and are divided on hundred people interested to buy, if you were to post 200 phones, the price would drop to $800 and $600 if not less (assuming auction).