It is the mobile users responsibility to take contact to the personal editor in the department /vd-area. Either to make sure that a solemn statement is filled out or to make sure, that the phone is registered for private use.
Personal editor in the department / vd-area detects whether the phone is used privately or not. If so, put a check mark , if not then the employee must fill out a solemn statement and sent it to HR for filing the individual case.
Salary Office draws regular lists from the system personal editor detects in and ensure that employees are using the private taxed on the phone.
It is the immediate supervisor when granting a phone and the employee signs an agreement with whether the phone it used private or not.