IOS (iPhone / iPad / iPod Touch)
In a market where the market leader is represented by a green robot, and the trailer (Blackberry) is likened to a notoriously addictive drug, the company with second-place market share has a level of customer loyalty and satisfaction often described as a cult. (All of which gives you some idea about how seriously people take these devices!) We are, of course, talking about Apple's iOS, the platform where it seems every new addition will sell more than the predecessor no matter what they do.
iOS is a slower-moving and far more tightly controlled platform than Android, with features designed to give a consistent, fluid, and controlled experience. As a result, the platform is great for doing things within Apple's designs, but beyond that it is by design inflexible. Because of the level of control Apple exerts over iOS, users cannot patch vulnerabilities until Apple releases an update - which in sometimes takes months and in many cases older devices are not compatible with the updates and so are never patched.
For applications there is the Apple app store, which Apple can be quite restrictive over. There have been many reported instances of applications being rejected for mysterious/unknown reasons, most famously Google's voice app in 2009. Because applications are all granted the ability to do everything allowed (with the exceptions of some things such as notifications and reading location) there are no complex permissions for users to keep track of and manage. While there has been at least one instance of a malicious app getting into the App Store, the most notable example was only a researcher's proof of concept.
Also of note though is the parallel ecosystem surrounding Jailbroken (where users have forcibly removed Apple's software protections) Apple devices. Jailbreaking gives users the ability to give devices new features, protect themselves from issues which Apple has not yet fixed, and install unapproved (or pirated) applications. At the same time, however, the removal of these protections potentially leaves users more vulnerable from a security perspective, as happened with the ikee worm in 2008.
iOS devices are a good balance when it comes to security, but this does come at a cost of flexibility that more experienced smartphone/tablet users may not like.
Windows Phone 7 and Other Aspirants
There are numerous other potential contenders in the smartphone space, most notably Microsoft's Windows Phone 7, but also including the Linux Foundation's Meego and Samsung's Bada. Symbian (formerly pushed by Nokia) and WebOS (formerly from HP) may in future rise or reappear as contenders, but at this stage they have both been dropped by their main proponents and open-sourced and so we will wait and see.
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