Priority call

Add a priority digit as a prefix or suffix to phone numbers, allowing the receiving device to filter calls based on their apparent importance. A default priority (say 5) may be assumed when the priority digit is not used.

The use of the priority digit is based on trust, but it will assist in screening out many inappropriately timed calls. You could set your phone to Bored, Regular, Busy/Dinner, Meeting, Sleeping, Movie/Don't Interrupt modes to reflect your current activity, but it would still be possible to receive a call in an emergency (preferable turning off or unplugging the phone).

Abuse could be handled by adding specific repeat offenders to a ban list, or automatically deprioritising calls from certain numbers. These would be special features of receiving devices.

Bonus side-effect: legislation could force all cold-callers to use the "Priority 0 Cold Caller" priority.

Extension: the priority digit concept can be extended to any communication where the target is addressed by a number and no special meta-data field is available. Many communication media (including instant messaging) could benefit from a priority indicator.