A web service would be useful for me as well. I'd like to do things like: forward calls to work at start of workday, cell when at lunch, remove forwarding at end of workday. DND activation and deactivation at certain times which vary depending on day of week. Given a web service I could set up cron jobs to perform these actions.

Another thought would be to come up with a list of all desired actions and make them controllable via whichever frontends can accept the needed parameters and returned data: web panel, web service, SMS, and telephone/voice interface.