There are two methods to do it .Choose the best method you like.
Method No.1: Changing Registry Values (Harder)
1. Run Registry Editor by typing regedit in the Start Menu search box or go to Start and select Run.
Type regedit in the window and click "OK".
2. Navigate to the following registry key:
3. Click on Edit -> Find or press Ctrl-F to bring up Find command to search for ZuneDriver.
4. In the right pane, edit the following registry values.
*Change ShowInShell from 0 to 1.
This enables Windows Explorer to show the device when plugged in
*Change PortableDeviceNameSpaceExcludeFromShell from 1 to 0
*Change EnableLegacySupport from 0 to 1.
This enables Windows Explorer to detect the device when connected.
5. Connect your Windows Phone 7 to your computer, and close out the Zune application.
Go to my computer.Now you can see your Windows Phone 7 device as a mass storage device.
Method No: 2 Using Windows Phone Usb Enabler (Easy)
1. Download Windows Phone USB Enabler From here (80 KB)
2. Run The Software.
3. A window appears like this.
4. Click On Enable.
5. If You Don't Want To Use Your Windows Phone As Mass Storage Device Click On Disable.
Congratulations You Have Successfully Enabled Mass Storage Access On Your Windows Phone 7.
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