The purchase of a new i9500 S4 smartphone-Priceangels.com

The world's largest retailer unveiled a i9500 S4 smartphone trade-in program in the U.S., just in time for the anticipated new iPhones. The move is likely to increase the competition among retailers that allow customers to swap their old phones for a credit to buy a new phone. If you don't want to be tied down for two years with a cellphone contract, the Nexus 4 is a great choice. A 16-gigabyte version of the device is available for $249 without a contract, and it will work with AT&T and T-Mobile's networks.

The only reason you may not want to get the Nexus 4 is because Google will probably come out with a new Nexus phone in a month or two. But if you need a phone with no contract right now, the 16 GB Nexus 4 is an excellent choice.Along with the new phones, Apple has recently launched a new iPhone in-store trade-in program. The program will lower the upfront cost of a new phone for people already using an iPhone, and help Apple sell more devices—a key priority amid Android’s ongoing dominance in the U.S. smartphone market.

The new program expands on an already existing online option that offers gift cards for old devices, and it comes as analysts are projecting big growth in the sales of old phones. The research firm Sanford C Bernstein expects the used smartphone market to balloon to 247 million devices over the next five years—it’s now just 53 million. While the smartphone market gets set to reach 1 billion devices this year, much of the growth is being driven by developing nations, where cheaper options than the top-of-the-line iPhones are in demand—and where used smartphone sales are strong. 

Cell phone providers already offer buy-back programs on a range of Air Gesture smartphone handsets, and in the U.S., competition has been heating up, with AT&T, Verizon and T-Mobile recently launching new trade-in deals. In Canada, Wind Mobile has announced its own in-store trade-in program, and in the retail sphere, Wal-Mart is soon to announce its own such program. Only an estimated 15 to 20 per cent of people currently use buyback programs, but some analysts say that figure will grow as companies vie to cash in on the resale market.lfj4D3ss2 

It’s all good news for consumers, but the deals generally come with a few hooks: they require you to sign up to a new plan, and buy that new device. Cell phone carriers also determine the price they’ll give you for that old iPhone 3 or Galaxy S.A recent South Korean report found that the smartphone addiction rate was 18% among teenagers. Dr. Jonghun Lee, a professor of psychiatry and the study's lead researcher, presented the findings at the American Psychiatric Association's annual meeting this summer. 

He stressed that the more smartphones are overused, the greater the risk for severe psychopathologies in adolescents. Those who are dependent on them experience anxiety, insomnia and depression. Some self-aware teens are realizing the toll that checking their smartphones is taking on them. An 18-year old girl told The Wall Street Journal recently, "I hate doing it, but I can't help it... Why did I buy a smartphone? Sometimes I stay up all night using Facebook and Twitter. I quickly became addicted."

A Pew Research Center study found teenage smartphone usage increased 23 percent from 2011 to 2012 and that 37 percent of teenagers owned cell phones for sale last year. Dr. Lee says that the number of adolescents who are addicted will go up, because the popularization of smartphones is an inevitable social trend. And the younger they are, the more vulnerable they are.