The number of IPTV subscribers will more than double every year from 2005 to 2009, when it will reach 68.9 million worldwide, according to the latest report.

A new study from market research firm Infonetics said that there are many challenges to overcome before IPTV goes mainstream, but that many of those hurdles are expected to be cleared soon. 

IPTV service revenues and service provider capital expenditure are set to increase dramatically, according to the report. Sales of IPTV equipment are forecast to jump from $371m in 2005 to $6.8bn in 2009.

"IPTV is still in the 'kick the tyre' phase with service providers doing trials rather than mass deployments, but there is no question that IPTV is going mainstream," said Jeff Heynen, lead author of the report. "The only question is the timeline."

The deployment of IPTV has proved far more complex than any of the proponents predicted, according to Heynen.

"The technical hurdles are well known, but the regulatory issues are less predictable," he said.

"Legislators are asking how they should treat and regulate IPTV, while content owners are asking how best to take advantage of these new markets."

The speed of deployment will depend on the answers to these questions, concluded Heynen.