SO you want to buy a new Apple iPhone, Samsung Galaxy, HTC phone or whatever suits you. What are you going to do with your old device? You could, like many people, just tuck it in a sock drawer or hand it off to a family member. Or you could trade it in for cash to get a discount on whatever new phone you buy. Often, the money you make trading in or selling a phone will cover a huge chunk, if not all, of the price of upgrading to a new phone. Yet lots of used phones are never sold. A study by OnePoll, a research company, found that Americans are hoarding about $34 billion worth of used cellphones. That's a lot of money that could be used toward upgrades. There are plenty of ways to sell an old phone, like mailing it to a reseller, handing it to a cellphone store or putting it up for sale online. I have used several approaches to selling used phones, online and offline. Two things to remember before you ditch the old phone: First, back up your information. Second, always make sure to erase all contents of the phone before shipping it. You don't want the phone's new owner getting access to your selfies and text messages. Gazelle - Gazelle offers a popular online trading program. It allows you to select which phone you want to trade in, then it presents an estimate of how much money you could get. First, visit Gazelle.com and select "Sell cell phones." Next, pick the brand, model, carrier and capacity of the phone. For example, iPhone owners should select "Apple" and then the model, carrier and capacity, like an AT&T iPhone 5 with 32 gigabytes of storage. Then describe the condition of the phone. If it has signs of wear and tear, select "Good." If it is damaged, select "Broken/Cracked." If it is shiny and unscathed, select "Flawless." Gazelle will then generate a quote based on the condition and model of the phone. An AT&T iPhone 5 with 32 gigabytes of storage, in good condition, for example, will go for at least $145. If you like the offer, choose how you would like to be paid: a check, Amazon store credit or PayPal. You can have Gazelle mail a shipping box, or you can print out the label and ship the phone with your own box. Then pack the phone and ship it. Wait a few weeks for Gazelle to receive and inspect the phone. Once it does, it will send an email with the final offer. You can accept the offer and get paid, or reject it and have the phone shipped back to you. EBay - Another popular method online is to put the phone up for auction on eBay. Because the older phones on the website are generally bought by other people as opposed to a reseller, the selling price for a used phone tends to be higher. First, visit eBay's webpage for used phones: pages.ebay.com/ebayforthewin. Select your phone model and click "Sell Now." Log into eBay with your account information and select the details for the phone: the carrier, storage capacity and condition (new or used). EBay will generate an estimate for the phone's general selling price. For example, eBay says an AT&T iPhone 5 with 32 gigabytes is selling for $207. Continue reading the main storyContinue reading the main storyContinue reading the main story You can add photos of the phone, edit the description and starting price, and then state how much the shipping will cost. Then list the phone on eBay. Once the auction finishes, wait for the payment to come through and then pack and ship the device. Retail Stores - A quicker way to get cash is to just take the phone into a retail store that accepts old phones. Plenty of cellphone stores accept trade-ins, including AT&T, Verizon Wireless and Sprint. Another good bet is Best Buy, one of the largest electronics retailers, which accepts used phones and sells new phones compatible with all the major carriers. At Best Buy, you simply go to the cellphone department and hand the phone to an employee. The employee will check the condition of the device and test to make sure it works. Then Best Buy will offer in-store credit or tell you how much a new phone will be discounted in exchange for the older device. Currently, a black AT&T iPhone 5 with 32 gigabytes is being quoted at $225. That's a lot more than what you'd make by throwing your old phone into the sock drawer.