The largest VOIP companies in America today are the cable companies, ACN (pyramid scheme with a few million VOIP customers), Vonage (a first mover) then a few dozen minor players that are near the half million customer mark. IMO its a big (but unsurprising) marketing failure.
VOIP as a product never really made it into the home, despite all its features and enhancements. Instead, it is limited to the realm of businesses, where it is in most hospitals, medical facilities, chain stores, call centers, and so on.