Handle9: If they want you to have a mobile they should either provide you with one or pay for yours via an expense claim.
The problem is that noone wants the hassle of carrying two phones with them, and some companies may be reluctant to fund a mobile phone by means of expense reimbursements due to a desire to get discounts by bundling their company mobile fleet onto a collective account.
I guess the only answer is for employees to stand firm and tell their employers that although lodging expense claims for their own personal mobile is likely to be more expensive than having a company mobile, they are simply unwilling to carry a separate company mobile if one is provided.