on-call duties :: to pay or not to pay

at work, we are talking about setting up a duty pager and a group of
us will join the rotation to be on-call 24x7x365. Some of us don't
think, or think the boss won't like, that the rest of us actually want
to be compensated for the on-call duties. To me, it makes sense to be
compensated for the inconvenience of carrying it, and also be
compensated for the excessive time working off-hour by comp-time or
cash.
A strong counter argument is that labor laws categorizes most of IT
professionals as exempt, in that we can't bill for hours outside a 8-5
work day. Many employers forget to see/emphasize/respect the other
side of the token. That is, the exempt status would be void if an
employer ducks our pay if we take a few hours off here and there.
Most don't deduct pay, but they frown upon and ask you to make up the
time. As a result, most of us opt not to take random hours off. Plus,
at smaller places, your chores pile up and your projects get delayed.
In the end, your performance (real or in the eyes of the boss-man) is
hurt, so are the salary and upward movement on the corporate ladder,
in turn.
It gets even murkier to us laypersons if on-call duties is actually
part of your job description. Does that entitle an employer to get you
work whole weekend plus a full week? what do you think?