I am required to carry a beeper 24 hours a day, every day of the week for my job. I am occasionally called on my vacation, holidays and other days off. When your employer requires you to be on-call but does not require you to stay on the company's premises, the following two rules generally apply. On-call time that you control and use for your own enjoyment or benefit is not counted as payable time. On-call time over which you have little or no control and which you cannot use for your own enjoyment or benefit is payable time.
Disputes usually boil down to the slipperiness in the definition of control and use of time.
If the occasional beep beckons you only to call in to give advice, but you are otherwise free to spend your time any way you want, your employer need only pay for the time you spend answering the beeper. This means that if you receive a paid vacation, it's because of custom, not law. And just as vacation benefits are discretionary with each employer, so is the policy of how and when they accrue. It is also legal for employers to prorate vacations for part-time employees, or to deny them the benefit completely. Employers are also free to set limits on how much paid time off employees may store up before it must be lost or taken.