Google voice is a service that give you a phone number which can be used to take calls from multiple phones, receive voicemails, send SMS and a host of other features. How much does it cost ? Nothing !!
Google Voice was formerly known as Grand Central (Yes, Google buys all ! ). It uses VOIP to link the users phone numbers and gives me additional features that may not be offered by traditional cellphone providers.
Users will be allowed to choose a phone number among many area codes. When someone calls this phone number, the user can choose which of his phones ring or if it should use voicemail. Also has the ability to switch phones in calls, record calls, call forwarding, conferencing, text messaging to name a few. Check out the video below.
Google Voice is still open only to GrandCentral customers but you can request an invitation by filling the form.