In Russia we do the same, but the important distinction is that generally SLAs differ too. Companies require (and expect) better level of service and tech support, so they pay more. Also, from what I've heard — comparing to natural persons — companies cause a bit more work for accounting departments.

Note: I don't know about telephony (they do charge more, but I don't know about their SLAs), but it is true for ISPs (I work for one as a programmer).

It is same in many other countries too, just because business phones are used much more often. It also hard to reuse such phone number, which is listed in many places: it will be "hot" for years.

Now, it is time to validate your home landline phone. Are you really doing no business over it? ;-)

I suggest that the cost to provide the service is either exactly the same thanks to amortization of equipment or only marginally higher for a small business with a single line.

Everything else is just the way they create price discrimination and exploit the customers' perception of value, much the same way that Microsoft have sixty-three jillion versions of Windows.