I suspect from reading between the lines of your post that you really want something that will 'legally' satisfy your companies requirement that you be available on call, but making it as least intrusive on you as possible. If it is a job requirement I would think you would want something easy for the 'customers' trying to contact you rather then having them jump through hoops because you feel being on-call is somehow unfair? I know this can be a sore point for many employees but having been on both sides of that equation and requirment I think a more professional outlook on the situation might be worth considering. Cell phone with voice mail is what I would recommend.
Lefty