Alright, everyone. This is of something you should take note. Google acquired GrandCentral and is now pursuing using the service for themselves. Luckily I have received my Google Voice account and have my own Google phone number, yay me. Now let me actually get to how this could help you out.
If you have multiple phones, say a house phone and a cell phone, you can set up Google Voice to ring the house phone, cell phone, or both depending on who calls. If you aren't able to answer either phone, then the personalized voicemail for that person will play (if you set it up). So you can greet them specifically the way you choose and they can leave you the message.
If you are away from your phone and would like to check those messages, you will be able to do so online via Google Voice. You can sign in and read/listen to those voicemails. Yes, I did say read the voicemails. Google evidently has software that will guess at what words are being said and provides you with a rough transcript to read. I believe it does a pretty decent job. If you wanted to take it a step further, you could even embed those voicemails online for others to listen to them. That's just a warning for anyone who would choose to leave less than decent messages in my voicemail.
Google Voice also enables you to SMS online with your contacts. You can send them from your computer for free, and you should be able to reply to them for free. That's if you avoid actually sending or receiving them with your own phone since mobile rates would apply. As I understood the instructions, you can avoid sending the messages to your phone by not indicating that your phone is your mobile phone. Use this information at your own risk. I won't pay for your mistakes.
There are many more features that I have not had the pleasure of trying out just yet, but let me name a few just to get you curious: ListenIn, Call Record, Call Switch, Call Screening, and Call Blocking. Those are just some of the nice features that you should really look into. Comment if you want to know more, or email me if you prefer to do that. firstname.lastname@example.org
Google Voice About page: http://www.google.com/googlevoice/about.html