Hundreds of thousands of iPhone owners will be upgrading their existing iPhones to an iPhone 4 which will leave many wondering; “What do I do with this old iPhone?”  Luckily, we have some answers.

While many have heard of people selling their old iPhones for hundreds on eBay, there are actually many great options. Cnet.com recently did a writeup on several businesses that could net you some serious cash by selling your old iPhone. Tech resellers Gazelle.com and NextWorth.com both pay a set amount based on the type and condition of your phone without the hassle of an auction. While they likely won’t give you the best price, they are the easiest.

For those who don’t want to deal with shipping, there are several local alternatives. Electronic retailers Radio Shack and Best Buy will reportedly have offers to help your wallet by bringing in your old phone. Craigslist also lets you sell your iPhone locally, and by avoiding the resellers, you can likely get a better price.

It doesn’t stop there, be creative. Try options like newspaper classifieds, school bulletin boards, and word of mouth. Spending a little time could get you a lot of spending money.