With services like Google Voice, nobody should need to carry two phones (one for business, one for personal) and there should certainly not be any demand for dual-SIM handsets. When you join a company, they'll assign you a new Google Voice number. You can control when such a number reaches you at your mobile and when it forwards to your desk phone or voice mail. If/when you leave the company again, the number is simply deactivated. No cost to the company, no extra physical device to carry and no fuss on termination.
Mokalus of Borg
PS - They would still need to set you up with a phone on your desk.
PPS - And reimburse you for company calls on your mobile.