The iPhone is still going strong and with the release of a couple of new iPhones earlier this year - iPhone 5s and iPhone 5c - millions of Americans continue to upgrade to the new devices. A recent study conducted by SellCell.com, a phone sales data aggregator, indicates that Americans have spent over $5 billion dollars to upgrade their iPhones in2013.

For the average iPhone owner, an upgrade to the latest model will cost $151. For most wireless carrier plans, this happens roughly every 2 years. Doing the math, SellCell.com came to a figure of about $5.4 billion, which is spent each year on iPhone upgrades alone.

While the figures may seem surprising, everything actually makes sense when put in the right context. The U.S. is one of the leading countries when it comes to smartphone sales and the numbers seem to be growing every year. Given that Apple devices account for almost half (41 percent) of the total smart phone market in the U.S., $5.4 billion for iPhone upgrades makes perfect sense.

Smartphones are becoming a necessity for most Americans as more individuals are starting to use mobile devices in lieu of laptops and desktops for an increasing variety of tasks such as online shopping and browsing. Aside from the obvious factors that include more power, higher screen resolutions and new features, Americans are also willing to pay generously just to get their hands on the new "it" device out in the market. For a large part of the population, this usually means the latest iPhone.

With people becoming more attached to their smartphones, wireless carriers have also started making the process of upgrading to a new smartphone a whole lot easier. Companies like AT&T, Verizon and T-Mobile have been competing for market share using added perks like early upgrade programs to lure in more customers. Aside from the early upgrade programs, carriers have also been generous with easy-on-the-pocket payment plans that spread out the cost of a new smartphone over the entire period of the contract. 

Given that smartphone sales are expected to go up in the coming year, it seems likely that Americans will spend even more to upgrade to the next iPhone.