Google Voice is no longer available by invite only. Google today announced that Google Voice is now available to all U.S. customers. The service gives customers a virtual phone number which they can then link to their own home, cell and internet phones.
Google voice also allows SMS messages to be sent to the users account, provides voicemail services free of charge and even allows for a speech-to-text transcription service to be utilized with no cost. Users can also take advantage of very cheap international calling through money they can load onto their account.
Google Voice is even available as an application on various mobile phones, unfortunately Apple only allows an HTML5 app to be used due to their own restrictions placed on the app which stops incoming calls to be made in the background...sigh.
Head over to Google.com/voice to get started.