Simple! Draw straws... the guy who draws the "short straw" loses. ;-)
On a more serious note. We have a monitoring system that pages all of the sys-admins whenever something goes down.
We have a good bunch of people who are on top of things. Nobody is compensated for logging in with VNC and restarting the mail server but people ARE compensated when say a hard drive crashes and it requires a trip down to the colo and a RAID rebuild or something.
Most companies I know of do pay for the sysadmin cell phones or gives a good discount. Depends on if the phone is for personal use as well. I've also seen company issued laptops and in some rarer cases broadband internet cards.
In the REAL world... there's a PC around or a hotspot (be sure to THINK and encrypt your stuff traffic) around somewhere.
The reality is... right now most people are happy to be gainfully employed right now and when you love your job... its just PART of the job.
The only REAL problem I've heard of (in regards to perks) was with an employee who was absolutly OBSESSED with his Red Swingline stapler. Management wouldn't listen, took the stapler away, and as a result the employee lost it and burned the whole place down!
(tongue in cheek reference) ;-)