Windows Phone 8.1 release date: Microsoft’s newest mobile OS, Windows Phone 8.1, is presently available in the Nokia Lumia 635. It’s personal assistant feature “Coratana,” which rivals iPhone’s “Siri” will be available in the next few weeks.

The Tech Times reports that the no contract model of the Nokia Lumia 635 via AT&T and T-Mobile is now available for pre-order from Microsoft.

According to the Windows Phone website, Cortana is the most personal smartphone assistant and is powered by Bing.

“She gets to know you by learning your interests over time. She looks out for you, providing proactive, useful recommendations. And Cortana keeps you closer to those you care about the most,” writes the WindowsPhone.com description of the feature.

WP Central notes below some the notable but small changes in the Windows Phone 8.1:

- Signal strength, data connection, Wi-Fi, Battery, Location and more all remain on the screen; they no longer auto-hide
- New People Hub redesign with smaller fonts
- Phone history now groups repeat calls from a user with ‘(#)’ representing number of calls
- Speed Dial is finally here under Phone

To see the complete list of changes, you can go here [https://www.wpcentral.com/windows-phone-81-review]

Specs of the budget-friendly Nokia Lumia 635 include a 4.5-inch display with a 480 x 854 Gorilla Glass 3 ClearBlack. The unit has a pixel density of 281 ppi and is also powered with a 1.2GHz quad-core Qualcomm Snapdragon 400 processor, Adreno 305 GPU and 512 MB RAM. The device has 8GB of internal storage.

Tech Times noted that camera capabilities of the Nokia Lumia 635 include a 5-megapixel-rear camera that can record 720P HD video. Battery for the unit comes in a removable 1830 mAh battery and provides up to 14 hours of talk time and up to 648 hours of standby time. Dimensions for the Nokia Lumia 635 are 129.5 x 66.7 x 9.2 mm and it weighs 134 grams.

The Nokia Lumia 635 is being sold for $99 (AT&T version) and $129 (T-Mobile version). Both prices are for the no-contract versions of the phone.