A Government Circular in this regard issued recently by the General Administration Department had been sent to all departments, government sources said.
The staff unions, however, voiced resentment over clamping such an order "unilaterally" without consulting the employees.
The circular said there had been complaints that public often failed to receive proper service from offices as employees were often found making or receiving personal calls on their handset.
It urged employees to avoid making personal calls except during extremely unavoidable circumstances.
A staff union leader said this circular had put the employees in poor light before the public.
If the government had a feeling that the use of mobile phones affected office work and delivery of services, the issue should have been discussed with the employees' organisations before slapping a circular on them, he added.