Managing who gets alerts - shifts and rotations

We're in the process of migratng from Big Brother to xymon.

I'm wondering what folks are doing about handling on-call paging shifts? We have a complex schedule of on-duty techs plus weekly rotations of oncall people for various teams. We've tried to incorporate the schedules into our rule sets and it is getting too complex to manage.

What are people using to manage this? In my ideal world, all my rules would be "page tech; wait 30 minutes, page on-call" but we've got to get some sort of scheduling software or script to manage who is at the other end of the email.

thanks Betsy