After six consecutive quarters of double-digit growth, the number of mobile broadband users slowed to 5% in the fourth quarter. That marked a steep drop from the 22% gain in the prior quarter.

Adoption of PC mobile data cards has surged in the last two years, more than tripling in 2007 and 2008. "That said, we've observed a significant deceleration in subscriber growth during Q4 2008 coinciding with the economic downturn, an indication that mobile broadband service may still be seen by many as a luxury rather than a necessity," said Serge Matta, comScore senior vice president, in a statement.

The firm suggested that Verizon Wireless might be best-positioned for a resurgence in mobile broadband after picking up two market-share points in the last year.

In terms of usage, comScore found that PC data card users were spending the same amount of time online as typical U.S. Internet users at about 90 hours a week during the fourth quarter. Among those with both data card and wireline connections, about 25% of their online time (22 hours) was spent using a PC data card.