iOS 5 has once again thrown open the debate about which mobile operating system is going to dominate the market in the next 12 months. Apple’s new effort isn’t due out until autumn, but is likely to land ahead of Android Ice Cream Sandwich, Google’s new-look OS pegged for release in Q4. So what does iOS 5 mean in reality for Google? And what about its less successful rivals, such as webOS, Windows Phone Mango and BlackBerry OS?

iOS 5 v Android Ice Cream Sandwich

Google’s OS has only been recently overhauled. Ice Cream Sandwich promises a unified tablet and smartphone strategy, which should help the best-selling OS go toe-to-toe with the iPhone and the iPad. To that end, iOS 5 is unlikely to give Google many sleepless nights.

The likes of iMessage, Reminders and improved Safari browsing are all very much welcome, but the Big G will point to the new Notification Centre being little more than an Apple take on an approach it’s been using since the T-Mobile G1 first reared its head three years ago.

iOS 5 v Windows Phone Mango

Mango should be hitting devices at around the same time as iOS 5 is getting into its stride. This plays into Apple’s hands, because while the improved Windows Phone platform offers better Live Tile information and deeper Twitter integration, it’s still only as good as iOS on paper. In reality, volumes are low.

This could be fixed by a string of new Nokia Windows Phones, which are expected for release by the end of 2011. But iOS 5, covering iPhones, iPads and iPod touches, is going to be on far more devices than Windows Phone can manage. Its new Twitter skills and vast app support also mean that no matter what Microsoft does now, Mango won’t be able to catch iOS for a very long time indeed.

iOS 5 v webOS

HP’s webOS update is set to break out into the wild in the next few months, with the Veer, Pre 3 and TouchPad set to give it a wide portfolio of devices with which to corner consumers. Ultimately, webOS remains a brilliantly realised operating system, with multitasking structure and Synergy aggregation that’s every bit as sleek as Apple’s efforts. But like Microsoft, HP is going to struggle to be heard above the din of iOS 5. Apple’s operating system might only be its equal, but the fact webOS failed to gain traction first time around means iOS 5 will leave it trailing in its wake.

iOS 5 v BlackBerry OS

Apple seems to have a thing about beating RIM, and with good reason. Smartphone charts show it’s now consistently trouncing the one-time mobile colossus, giving Jobs and co the belief that it can take on the traditional players and win.

iMessage acts as a direct challenge to the super-popular BBM platform, while new Mail improvements, including encrypted message support and the ability to flag important missives, attack RIM’s core work-based business. In going after RIM’s youth and enterprise customers, Apple is covering all bases. Add in the fact that the BlackBerry PlayBook’s specially built OS still lacks a native email client, and it’s clear that RIM should be deeply concerned about iOS 5.