People who have businesses. Even people who have personal businesses require themselves business cards, so that potential customers can easily contact them.
Technically it's unethical to charge more to customers who don't pay in cash, but it cost money for a business to accept credit cards and some small companies charge a credit card fee to compensate...
The most common one is probably "work". Most people are probably smart enough to figure out the "phone" part when they see something that looks like a phone number, and if they're not, do you really...
A business card is quite possibly the single most important piece of information you will ever give your client. The reason for this is people buy from people and its likely the only company...