I started looking into this a while ago, but then I left IT and was no longer on call.
I seem to recall something about IT being different in that you can be on call, and the compensation must be agreed to between the employee and the employer.
What we used to get was 1 hour of overtime for a weeknight of being on call, and 1.5 hours of OT for a weekend day on call. Any time over and above that I charged by the half hour. Sometimes I would have them dispute it, but as was often the case I would get paged while driving along Deerfoot, or while shopping in a store, so whatever time it took me to get to a place I could safely and securely make a call.....