According to the FCC, the VoIP subscribers is 21 million not including Skype users. These figures are part of the 31-page report, "Local Telephone Competition". The report uses data from 2008!
Of the 162 million voice lines, 21M are VoIP. Consider that cablecos probably represent almost half that number. Vonage is about 2.5M subs then. VZ's FiOS is VoIP, so that's about 1M. So the hundreds (probably thousands) of VoIP Providers amount to 8M lines? OUCH! No wonder they need more funding.
According toi the report (via The Register), only 2M lines were business. 19M were residential.