By Lou Carlozo, dealnews contributor According to a Gartner study, app developers earned an estimated $15 billion in 2011, up from just $5.2 billion in 2010. So, in our ongoing effort to stay on top of the times — and of course, the bargains — here's a look at the best deals on iPhone accessories, from free apps to discounts on cases for any style. Hello-Hello Japanese App Downloads Price: Free Lowest By: $15 Is It Worth It?: The iTunes App Store offers downloads of Hello-Hello Japanese for Apple iPhone, iPod touch, or iPad for free. Ōkina setsuyaku! (Big savings!) If learning Japanese isn't one of your New Year's resolutions, check out our daily roundup of free apps here. Missoni Colorful Horizontal Case for iPhone 4 / 4S Store: Target Price: $9.43 via coupon code "TGTHTT5Z" with $4.98 s&h Lowest By: $20 Is It Worth It?: The chic house of Missoni has been around since 1953, and its collections at Target are uniquely designed, functional products — not to mention, super desirable. Right now, this Colorful Horizontal Case for the iPhone 4 and 4S is $20 off retail, or at a 65% discount. Give your phone some fashionista flair for just $9.43 via coupon code "TGTHTT5Z". Bumper Case for iPhone 4 / 4S Store: Cellular Factory Price: $1.99 with free shipping via coupon code "QK4649" Lowest By: $2 Expires: January 10 Is It Worth It?: Made of environment-friendly materials, this white Bumper Case for iPhone 4 and 4S is also washable — and will protect your phone from, well, bumps! And hopefully bruises. All4Cellular Sale Discount: 15% off via coupon code "POTW" EXPIRED Shipping: $2 s&h Expires: January 9 Is It Worth It?: Take 15% off select iPhone and other cell phone accessories at All4Cellular with the coupon "POTW". Shipping will only cost you $2, so why not pick up a new case, Bluetooth headset, or charger? Pictured here is the AGF iPhone 4 / 4S Vandelay Premium Shell & Holster, which will set you back just $3.36 with shipping, and is the lowest price we could find by $4. JBL Micro Speaker System with iPhone Dock Price: $99.99 via coupon code "GODEALNEWS" with free shipping Lowest By: $63 Expires: January 6 Is It Worth It?: In a world of hi-fi pretenders, JBL is the real deal; their loudspeakers grace recording studios and detailed listening environments the world over. And this Micro Speaker Set for the iPhone features a remote, LCD display, AM/FM radio, seven independent alarms, and more. Front page photo credit: Business Insider Lou Carlozo is a dealnews' writer who covers green issues. He was most recently the managing editor of WalletPop.com, and before that a veteran columnist at theChicago Tribune. Follow him on Twitter — @LouCarlozo63. You can also sign up for an email alert for all dealnews features.