I just got my Voice over IP phone set up a few weeks ago through Earthlink.
So far, so good.
I can check and hear my voicemail via the internet. The are downloaded as WAV files so you can keep your messages for as long as you want. You can also check it via the phone like normal.
It lists all incoming and outgoing calls so I know who I talked to and when. If for some reason the cable goes out(hasn't in 3 years), it automatically forwards to my cell phone. Free options like caller ID, voicemail, call forward, all the stuff the phone company charges for.
Best of all is I have unlimited long distance in US and Canada for only $30 a month and the first month, set-up, and equipment was free. Only cost me $10 to have the convertor shipped to me.