Urgent Callbuddy will detect when someone is repeatedly trying to call you by monitoring how many missed calls you've received within a configurable time period. On detecting repeated missed calls it will set your phone's ringer volume to the maximum.
The time period and the number of missed calls are configurable, version 2 will allow you to configure block and allow contacts lists.
Currently only tested on Nexus S and Nexus One devices, but will probably work on a wide range of devices, it's free so there's no harm in giving it a try.
As with all my apps this product comes with no advertising and only requires permission to access the bare minimum of the functionality of your device and your personal data necessary to achieve it's purpose. At no time will this application upload any personal data or usage information (except crash reports) to an external server or database. I believe in making simple, functional applications with no hidden forms of revenue generation through exploiting the privacy of the end user. Simple applications for a simpler world.