The main thing is this ""We hold that when employees must use their personal cell phones for work-related calls, Labor Code section 2802 requires the employer to reimburse them. Whether the employees have cell phone plans with unlimited minutes or limited minutes, the reimbursement owed is a reasonable percentage of their cell phone bills." Even if the employee has purchased a personal cell phone plan that provides the employee with "unlimited" minutes and the employee does not incur any additional expense for his/her work-related calls, the employer must still provide a reasonable reimbursement to the employee."
Doesn't say about Data, which could be the bigger issue, but one would think that would be similar.