WAL-MART
From a robber who had his share with an Apple store.
the 3gs is much better for it's money iphone 3gs is better, i think. but it is very dear. it seems that you have enough money. if not, you can buy cheap phone instead.
You can buy accessories for iPhone 4 online at various retailers such as Wal-Mart, Target, Sears, JCPenney and Macy's. You can find accessories for iPhone 4 any occasion you may need.
Buy a used one.
Right now, you can get a cheap iPhone 4 from Sprint and AT&T. You can get one from AT&T for around $100.
Look on Ebay or Amazon
If you want to buy a cheap iPhone case then I want to suggest Gadgetzkart. They provide the best and premium quality iPhone cases at reasonable prices. So, if you want to buy an iPhone case for you any model of iPhone then, It is the best to Place for this.
YOU CAN'T buy an iPhone 4 because THEY DON'T exist.
Ebay, try get a seller refurbished one or a used one that is in great condition
If you are really looking for a place to find a cheap IPhone 4 whether the IPhone is used or brand new, then you should definitely check out the apple store.
You can buy an iPhone 3 case for cheap on eBay or amazon. They offer multiple cases that were used but are in great condition. Check out those sites today for good deals.
Yes, actually it's the only carrier you can buy the iPhone 4 from in the US.