As IPTV evolves beyond a telco-only play, the number of "hybrid" set-tops - those supporting legacy cable/DBS video services as well as IP-based services - are expected to accelerate at a rapid clip.

But just how quickly? According to a forecast from The Diffusion Group, shipments of hybrid set-tops could reach 17 million by 2010. In turn, IPTV subscriptions could jump from 280,000 subs today to north of 37 million by 2010 - with two thirds served by hybrid offerings, the research firm predicted.

Service providers other than the telcos are expected to spur much of that growth.

"Even though the telco-TV market now enjoys decent media and press attention, implementations of IPTV by digital satellite (DBS), digital terrestrial (DTT) and cable operators will probably dominate in the medium to long-term future," said Diffusion Group Consulting Analyst Herve Utheza, in a statement.