Grand Central has been adapted into what is now Google Voice. Google bought up 1 million phone numbers recently as it prepared to launch Google Voice to the masses. Earlier this week Google Voice began its public launch. Currently it is by invitation only (Google employed the same sort of social network marketing to create demand and build interest when it launched its GMail email service).

The central component remains the same as the principle behind Grand Central. Essentially you can have a single Google phone number which can ring to your home phone, mobile phone, work phone, or any combination thereof. As you move, change jobs, etc. your Google Voice number remains the same so you never need to update peers, friends, or family.

Google Voice offers a number of other useful features beyond single-number access though. You can receive voicemail in your email and forward or share it as you wish. You can customize which phones ring based on who is calling. You can establish different voicemail greetings depending on the group or individual who is calling. It also provides conference calling and call recording features, as well as the ability to switch between phones mid-call.

Google Voice is free (at least for now). As it is, it seems like it could be a sort of poor man’s unified communications for the budget-impaired. When you combine Google Voice with the upcoming Google Wave, it certainly appears that Google could put a dent in the unified communications market. Check out the Google Voice site for video demos of the features and functions. You can also click the link to beg for an invitation to the party.