CHECK THIS LINK TO UNLOCK THE "Unknown Sources" OPTION ON YOUR NON ROOTED ANDROID PHONE
Now you can install apps on your Android powered phone or device without having to get them through the Android Market.
Android Injector allows you to quickly and easily install apps that you have downloaded to your computer in the form of ".apk" files onto your Android phone or device. Some phones do not allow you to install apps from any other source except the Android Market. However, some app authors do not release their apps to the Android Market and elect to put them on other sites such as Getjar.com. Android Injector allows you to download apps from those other sources to your computer and then install them onto your phone from your computer quickly and easily via USB connection.
Just install the USB drivers for your phone or device onto your computer (check your carrier or device manufacturer for drivers), connect your phone to your computer via a USB cable, select any amount of Android app files (.apk) and click "Install to device". No rooting or any of that complicated stuff.
~~Credits Go To Kyle Dusang, Harmony Hollow Software~~