Not illegal, unfortunately.

Say three days off...

Pilot can be required to check his schedule "periodically" on his days off as long as he:

1) Has a 30 hour break somewhere in there.
2) Is not required to check his schedule within 10 hours of show.

This is work rules, not regulatory. Basically the company is assuming that anyone can check their schedule anywhere at any time on their phone, so it doesn't really interfere with contractual days off (except you can't go on an excursion out of cell-phone/internet coverage, which is actually an issue for of the Rocky Mountain folks). The company is also assuming they own your butt starting at 0001 on your first work day.