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Apple is now selling an unlocked version of the iPhone 4 in its online store, confirming earlier rumors which hinted this would be the case. The new iPhone 4 is the GSM model, which means here in the U.S., AT&T or T-Mobile only. The phone works outside the U.S. on any other supported GSM network offering micro-SIM cards for the iPhone 4.

Most importantly, the unlocked iPhone 4 is available contract-free.

From the makers of mobile app discovery service Zwapp, there comes OneMillionAppSchemes.com, a new initiative which aims to open source the unpublished custom URL schemes for iOS applications. For those unaware, a custom URL scheme is a way for apps to communicate with each other and do other smart things. For example, custom URL schemes allow other apps or Web pages to call the app, trigger it and send data to it, or even transfer data between lite and paid app versions.

Apple's built-in apps like Safari, the Phone app, the Messaging app, Email and others have URL schemes included by default. Developers using the iOS SDK can built their own, too. Unfortunately, though, there isn't a well-maintained master list of these custom URLs anywhere on the Web.

Just because Microsoft has its own mobile operating system called Windows Phone 7, that doesn't mean it's above using the popularity of Apple's iPhone to attract new users to its up-and-coming Bing search engine. For example, this week, the company highlighted a recently added Bing feature called "auto app discovery" by way of a company blog post that describes how the Microsoft search engine is a great tool for finding new iPhone applications.

A new report from Forrester focuses on the topic of building secure applications for the iPhone and iPad. Given iOS's popularity among enterprise and consumers alike, it's important for developers to understand the best practices for ensuring that mobile apps handle sensitive data appropriately. This is especially true when building apps for the financial sector.

But the finance and payments industry aren't the only ones who can benefit from a better understanding of security management - anyone building an app that handles customers' private data should be aware of iOS's data protection features and guidelines.

With this week's introduction of iOS 5, Apple's next-generation mobile operating system, owners of older iPhones are curious as to whether or not their device will support all the new features. iOS 5 brings a number of exciting additions, including a revamped notification system, deep Twitter integration, an updated version of Safari with support for tabbed browsing and reading lists, a more advanced camera system, a Newsstand app for managing newspaper and magazine subscriptions, a free messaging service for iOS users similar to BlackBerry's BBM, and more. In total, Apple has added over 200 new features to the operating system, the company says.

But will your phone run them?

In this continuing series here on ReadWriteWeb, we round up some of our favorite new applications for smartphones each month, specifically for iPhone and Android devices. This spring edition includes some major new launches on Android, like Netflix and Google Music, as well as some incredible technology leaps on iPhone, like the app which identifies trees by their leaves! As a bonus for this month, we've added a section with notable app updates and another featuring new tablet apps.

95,000 of the roughly 300,000 mobile applications that have ever appeared on the Android Market are no longer available - an app attrition rate of 32%. In comparison, 80,000 apps out of approximately 500,000 (or 16%) created for iOS devices including the iPhone, iPad and iPod Touch have similarly disappeared. This is a notable difference between the two marketplaces, especially given the Android Market's shorter existence.

Why do these numbers matter? For one thing, the app attrition rate is often a factor in calculating store sizes. More broadly, the differences also speak to the opposing cultures of the stores themselves. Many Android developers appear to approach app publishing as an experimental effort, not a business, and publishing and pulling apps far more often than those on the App Store do.

For users of Apple's iOS mobile operating system, there was much to be excited about in yesterday's keynote unveiling iOS 5, the next version of the OS for iPad, iPhone and iPod Touch. Deeper Twitter integration, wireless syncing across devices, and the ability to untether your iOS devices from the desktop have rightly got users anticipating the next OS upgrade.

One feature that is sure to please productivity geeks is Reminders, a new native task management app for iOS that works across devices.

Of all the new features announced yesterday at WWDC as a part of iOS 5, one of the more interesting options now available to developers is access to iCloud. Much more than just a MobileMe replacement service, the new iCloud will store and sync music, photos, apps, calendars and documents to all your devices, including your iPhone, iPad, iPod Touch and even Mac and PC.

But the service isn't being limited to Apple's own products, as it turns out - developers can use iCloud with their own mobile applications, too.

At WWDC this morning, Apple announced that its iOS mobile operating system, which powers iPhones, iPads and iPod Touch devices, is now at #1 in terms of market share. iOS has 44% of the total mobile OS market, compared to Android at 28%.

According to Scott Forstall, SVP of iOS software at Apple, 200 million iOS devices have been sold, 25 million of which were iPads, Apple's tablet computer released just 14 months ago.