Localytics iOS 5Since iOS 5’s debut on October 12, 31 percent of devices able to support the operating system have downloaded the upgrade, according to a study by Localytics.

iOS 5 has a large number of features compatible with older Apple builds making this one an enticing upgrade. These include iMessage, a real-time messaging service between iOS devices, Reminders, a new mail app, and more. The main feature reserved only for the iPhone 4S is the voice assistant app Siri. Even this was recently successfully ported to an iPhone 4 with iOS 5 installed.

Localytics, a software company analyzing applications, studied iOS device usage between the iOS 5 release date and October 17. Without considering iPhone 4S devices, which comes preloaded with iOS 5, nearly 1 in 3 devices with the option to upgrade did in just one week. Of that 31 percent, 36 percent were not iPhone users at all. In fact, they were iPad 2 users, soon followed by iPhone 4’s. The iPod Touch 4G brought up the rear at 17 percent.

In all, the iOS 5 upgrade is available to the iPad 2, the original iPad, 3GS and 4G iPod touches, and iPhone 3G’s and 4’s.

According to Localytics, app developers should be paying attention to the speed at which people adopt the new operating system. The company believes that with the increased amount of upgrades, we should be seeing app developers submitting their own iOS 5 compatible apps soon.