There still hasn't been an announcement that Apple will announce a new iPhone, but it seems highly likely. If you're one of those who can't wait to upgrade, what will you do with your old iPhone?

You'll probably want to sell it and get the most money you can get for it, and then use that money to purchase the latest iPhone model. So where should you sell your iPhone? Let's take a look at the places that will offer you the most value for your old iPhone.

Cash or Gift Card: Here's a question for you: do you want cash for your iPhone or will you take store credit for a future purchase? If you want cash, you should go through a website like Gazelle, Next Worth or Glyde. If you don't mind a gift card (or site credit), Amazon, Wal-Mart may work for you.

Which iPhone Do You Have? If you have the iPhone 5s or 5c, that's going to be the phone in the highest demand, but iPhone 5's will also get you a nice trade-in value. The more storage space you have, the more money you're going to get for your device. Also, if your phone is unlocked, meaning it can be used on any carrier, it's going to be worth more.

Side-by-side comparison: The Wall Street Journal recently published a new graphical way to see who gives the most cash value for iPhones. Glyde is offering the most cash for the three latest iPhone 5 models. Interestingly enough, if you have a iPhone 5s with 16 GB of storage on T-Mobile, Glyde will give you as much as $350 for it. Amazon will offer really great trade-in values for iPhone 5s and 5c, but it's going to come in the form of Amazon credit. Since Amazon doesn't sell iPhones with contracts, they just sell the full-priced unlocked ones, you won't be able to use your Amazon credit to buy the next iPhone at a discounted price with a new 1 or 2-year contract.

If you don't mind buying your next iPhone through another retailer and then using your Amazon credit for other products, Amazon is your best bet, but if you want cash, Glyde is the best option.

Lock in your offer soon: The sooner you can commit to selling your phone, the better price you're going to get. Make sure your phone is in the best possible condition and include all of its accessories as well.

Other places to sell your phone? You could try eBay, but you'll have to come up with the best price you think that eBayers are going to buy. eBay users tend to bid heavily on unlocked devices and many of them are savvy buyers and know when an eBay seller is trying to price gouge them. If you choose eBay, make sure to price your phone at a fair starting price that is slightly lower than other websites. This will encourage more bids on your phone.

What do you think about selling your iPhone? Have you ever sold one before? Let us know in the comments section below.