Ring Loud Contacts on the Android Market
Source for Ring Loud Contacts available on github.com

Ring Loud Contacts

Automatically maximize ringer volume for incoming calls from certain contacts.

** This app requires caller-ID. **

This is an Android app that maximizes your ring volume when certain numbers are calling (even if the phone is on silent mode.) These numbers are specified by the user. The user can add one of their contacts or specify a number manually.

The app can easily be disabled from the settings menu if the user needs true "silent mode."