"Voicemail like email, call routing, voicemail transcription, and more. All for free."
Google Voice is an awesome service offering a free phone number to forward to any of your lines (landline or cell). Here's Google's bulleted features:
There are several instances where this can be extremely handy. If you wanted a 2nd phone number for a small or side business to avoid using your personal one, you now have a free business line that rings to your same cell/home/work phone but has its own voicemail.
It's also helpful for those that constanty change phone numbers, where it be from moving locations or switching between carriers (less of an issue these days).
You can also choose a different area code from where you're living. If you have a friend or family member who is long distance from your area code, you can choose a number that is local to them. By doing this, it'll be considered a local call when they call you through your Google Voice number.
The only catch using this service with your cell phone is that all calls through Google Voice use your cell phone minutes, even if the other person is under what would normally be a free mobile-to-mobile connection. This is because you're call is going through Google, which isn't Verizon, AT&T, etc.
Another option of Google Voice is to use it as a replacement to your current voicemail. For instance, rather than paying $2.99 per month to use Verizon's Visual Voicemail service, you can set up Google Voice to replace your Verizon's voicemail for free. If you're fortunate enough to be using an Android or Blackberry smartphone, there is a Google Voice app you can download. Other phones, including the iPhone, can access Google Voice features through the mobile browser.
The following are Google's bulleted features for using Google Voice with your existing non-Google number:
Perhaps Google's videos would better describe what all it can provide. More info here.