Set Up a Switchboard
If you're expecting a lot of incoming phone calls, an answering service might be worth the investment: You'll seem more professional to customers, and you won't be roused from bed at the crack of dawn by callers who don't understand what time zones are.
You can have a live answering service (similar to the one your doctor uses) for $20 a month--or less, if you have minimal incoming calls. Another option is to do it virtually: For about $10 a month, you can get an 800-number-based system such as RingCentral that answers calls with an automated greeting, routing calls to you (or other employees or contractors) or to voice mail depending on button presses.
If phone calls aren't a big deal, consider a second landline or a dedicated cell phone that you can use for business: Adding a line to either is easy, and with a cell phone you can even share minutes under a family plan.
For a Little More: Get a Virtual Office
The world doesn't need to know you're working in your basement, so many business owners turn to a P.O. box for the official address of their company. A bare P.O. box, however, doesn't seem all that professional, and you can't receive UPS or FedEx shipments there.
Another option is a virtual mailbox service, such as that of Regus. With a virtual mailbox, you get a physical mailing address and someone who will sign for packages from other carriers. The catch is that people sending you mail still have to put a PMB code on the envelope, though it's less conspicuous than with a regular post office box. You pick up the mail once a week, or the service forwards it to you at cost. The plans cost $100 to $150 per month.
You can step up from there to a more serious arrangement: A virtual office setup gets you not just mail service but a live receptionist who answers the phone however you like, plus access to a physical space with offices, conference rooms, and even videoconferencing facilities. Fees can range from $250 to $325 a month.