I find Google Voice very convenient, and it seems to fill most of the use cases listed on other comments. If you have a Google Apps for Business account, you can get a phone number associated with your work account, which is nice to separate personal and work numbers. My work number only rings my corporate Gmail, which is open if and only if I am at work. Combined with a decent headset, the call quality is much better than cellphones. And, if you want, you can forward it to your cellphone when you are away from your computer. A very sad missing feature is that you cannot forward two Google Voice accounts to the same cellphone number, so you can't forward both your personal and your work numbers to your cellphone.
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I find Google Voice very convenient, and it seems to fill most of the use cases listed on other comments. If you have a Google Apps for Business account, you can get a phone number associated with your work account, which is nice to separate personal and work numbers. My work number only rings my corporate Gmail, which is open if and only if I am at work. Combined with a decent headset, the call quality is much better than cellphones. And, if you want, you can forward it to your cellphone when you are away from your computer. A very sad missing feature is that you cannot forward two Google Voice accounts to the same cellphone number, so you can't forward both your personal and your work numbers to your cellphone.