If you don't know about it already, Google Voice is a free service. It assigns a telephone number, then you can set up the phone numbers that you own to Google Voice so all received calls are forwarded to those phones. So, if you receive a call on the Google Voice number, it will ring each of the phone numbers (such as your cell phone and a home landline). In addition, you can set Google Voice as the voicemail service for your cell phone, giving you the equivalent of visual voicemail for free. (It also tries to convert the voice mail to text, which you can read before listening to the vmail, and it can be texted to you, and/or sent to you by email as well.)
There are other useful features as well - such as forcing numbers that are not in your contact list to announce themselves before the phone will ring through, or even automatically forwarding unknown numbers directly to voice mail.
Great service.