Well you first of all have to have the money to invest into buying the items (the iPhone's).
Which run at these prices:
-iPhone 2G 4GB, 8GB, 16GB   (2G = Second Generation)
4GB   - $295
8GB   - $350
16GB - $425

-iPhone 3G 8GB, 16GB White & Black (3G = Third Generation)
8GB   - $500
16GB - $700

**All items have to be brand new**

So now this is where the guide starts at.
You can either buy an iPhone from the Apple store by activating in the store or buying it off eBay, craigslist, or another local classified ad website.

With the iPhone 2G's you can unlock them either by Turbo-Sim, X-SIM which cost money or the free way by using ZiPhone.org which is totally free no charge.

With the iPhone 3's you cannot unlock them with ZiPhone.org due to a programming flaw, but can be unlocked by X-SIM and Turbo-Sim.

When iPhone's are unlocked they always obtain an extra 100 or 200 dollars to the auction making you, the seller, richer. So take advantage of this guide and situation because iPhone's values go down within 3 or 4 months and in this time period you could be making yourself thousands and thousands of money just from knowing my knowledge.

Enjoy!
Skateboard_Crazy