Jane “on-call” time, compensable

Jane is a Senior Help Desk Technician that is considered a non-exempt employee. Her normal work hours are Monday-Friday from 8 am – 5 pm. Because she is the primary “escalation person” for her company, she is required to carry a company cell phone with her until 10 pm, Monday – Friday when she is not at work. Escalated calls occur on an ad-hoc basis, and she does not have any additional restrictions, she simply needs to answer the calls if they come in. Is this “on-call” time, compensable?