iOS 6's Do Not Disturb feature has an option that lets the caller through if they call twice, which can achieve a similar effect, though not only for a specific group.
Still wouldn't have helped for the recruiter who redialed me 6 times while I was attempting to read a 400-page PDF manual (incoming calls dump you out of the Adobe PDF reader and you've got to re-find your place in the document), while attempting to recover a melted down server in the colo (hadn't anticipated this, laptop was at the office).
Solution: tell the recruiting firm never, ever, ever to contact me again.
Second solution: take off and nuke Adobe from orbit.
Third solution: ePub for docs, people. It's multi-form-factor fungible, and the readers are vastly, vastly more functional than anything built for PDF.
