For younger consumers, it's becoming increasingly normal to have only a mobile phone, no landline. To get medium to large businesses to the same state would be trickier. They have different needs, such as department phone numbers, or office-hours reception. In these cases, customers are trying to reach a generic role, not a particular person.
What you need in this case are virtual phone numbers that redirect to a managed set of mobiles. Call transfers might be more of a problem that way, as would billing for business calls, but I'm sure someone can figure those problems out. As for outgoing calls, you need to be able to mask an individual's mobile number with the company number on caller ID. Given these difficulties, it's no surprise most companies buy key employees their own business mobile plan.
Mokalus of Borg
PS - It's possible Google Voice can serve all these needs.
PPS - But it remains to be seen whether it's effective for a large business.