AT&T dominates the market for commercial ISPs, delivering about 20 percent of Internet traffic to businesses during September, according to ComScore.

Source: ComScore

Verizon is the second most popular ISP for businesses, delivering about 12 percent of page views. It was followed by CenturyLink, which has a 7 percent share, tw telecom and Level 3, which each have a 5 percent share. Sprint had a 4 percent share.

Comcast is the highest ranked cable operator on ComScore's rankings of the top commercial ISPs, delivering about 5 percent of Internet traffic to businesses in September.  Cox also made the list, with a 3 percent share of traffic in September.

While providing high-speed Internet and voice services represents a small fraction of the revenue for cable operators, Comcast, Time Warner Cable, Cablevision, Cox and other MSOs have said that providing commercial services is one of the fastest growing parts of their operations.