Here is a nice app that can used to add ringtones to your WP7 device.
The applications has two components
- Desktop application – used to build a custom XAP package with 5 custom ringtones you select from your computer (Requires .NET 4.0 Framework)
- XAP application – to be deployed to your WP7 to install custom ringtones to the system
- Ringtones have to be in the WMA format at 48KHz as required by the OS. We recommend using Expression Encoder 4 (free) to transcode any MP3s.
- Currently, to deploy the XAP you will have to use the Microsoft “Application Deployment” tool with the Windows Phone 7 Developer SDK. In the future, we hope to make available a standalone deployment solution for homebrew apps.
Note that you will need to unlock your WP7 device first. Other WP7 Tips