We now have the first WP7 homebrew application taking advantage of unlocked phones - a Windows Phone 7 custom ringtone manager.
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.
U need to unlock your phone to Deployment Phone first by using MFG tools, before u can deploy the ringtone using Windows Phone 7 Developer Software.