I think that would depend on the nature of the business, and if they will be in an office location during all work hours. If you were a plumber, a cell would make more sense, because if you are good at it, you are often out of the office on service calls. Most people I know that own their own business do so because of the flexibility of hours and work location. I know several psychologists who do competency evaluations. They are generally in their office or an office type setting for the interview itself (usually over webex) but can otherwise work where ever they want. So a landline wouldn't be idea for that. If your business is a bakery, and you will have a brick and mortar location, then sure, a landline would work.