Generally, if you are considered on-call you are not considered working (in most cases) thus you will not be paid for on-call time. To further explain on-call time it depends on how free the employee is to use the on-call time for their own purposes. Employees who are required to remain on the employer’s premises and are not able to use the time for their own purposes must be compensated. Read more about work hour law on the US Department of Labor's website.