i have a friend that uses it and the sound is about the same as normal telco , he also pays like $20 a month for a single outgoing only pots line in his house .. good to have to say , call 911 if the power goes out
my brother lives on the other side of the country and we both just use a voice chat program on our computers , it's free and works fine ( their are differnt ones out their , just need to work out whats good for you ) , in theory , if everyone you knew was online , you should never have to pay a phone co. But then calling for pizza becomes a problem

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the big phone companies are doing everything and anything they can to prevent the spread of voice over ip that is NOT controled by them , and they are loosing ( recent attempts at passing some bills in congress died ) , i guess they are concerned about not being able to charge 10cents per min , per mile when it costs them .005 cents to route the call and only during the connection ( made up numbers , but you get the idea )
simple fact is that the internet and the phone system is basicly the same thing! , both run through the same switchs and routers , just the pots system uses a differnt protcol and in some cases differnt lines , but not that often anymore. Call a friend in another city with pots and visit a web page in that same city and odds are 98% of the "packets" are going through the same hardware.
it allways amazes me how telco companies are "compeating" with ISP's for customers , when it's the tel co thats renting the high speed lines ( T1's OC3's etc ) to the ISP's in the first place! just look at DSL .. ever wonder why no matter who you get dsl from you still need to be X feet from the telco's switching station