Depending on the telephone company that provides your service and the particular law in the state where you reside, you may be required to list your home telephone as a business telephone if you do any work out of your home. If this happens, you should expect to see your telephone bill rise because the rates for business phone services are generally higher than those for residential services.
Just what level of business activity will make it necessary for you to list as a business varies from telephone company to telephone company and from state to state. It's pretty safe to say that you will be required to list your telephone as a business if you include your home telephone number in advertisements. Beyond this, you may have to have a business listing if you include a home telephone number as a business number on any company materials distributed to the public (such as stationery or business cards). Some states will even require you to get a business listing if you do business over a home telephone!
If you are in doubt about whether you'll need a business telephone listing or not, you can always ask your telephone company. But you may end up regretting doing this if the answer is not what you wanted or if you disagree with how the telephone company is applying its rules or interpreting the law. Instead of asking the telephone company, you may be able to get the needed information by consulting a network of local business owners (such as members of your Chamber of Commerce or other business group).
While the likely higher rates of a business listing are the downside, such a listing can also help grow your business. It gives your business higher visibility in the "white pages" and allows you to gain access to the yellow pages, which can be an excellent marketing tool for your business.