Although currently most companies buy their own telephony equipment and manage it on-site, by 2006 half of all businesses will benefit from selectively outsourcing internet protocol (IP) telephony services, Gartner has predicted.

The analyst firm pointed out that, with such growth potential for IP telephony services, providers are offering an increasingly wide range of services.

Gartner expects managed IP telephony and IP Centrex to become the most successful IP voice services for US businesses over the next three years.

IP Centrex refers to hosted network voice services with private branch exchange (PBX)-like functionality and IP features, provided over carrier networks rather than IP customer premises equipment.

According to Gartner, key factors favouring an IP Centrex choice include a preference for ongoing operational expenditure over upfront capital expenditure, together with a lack of internal telecom management voice expertise that can be easily applied to IP voice.

Steve Koppman, principal analyst with Gartner's network services research group, said in a statement: "Managed IP telephony will be the most widely adopted service provider IP voice approach for US businesses. Softswitch-based IP Centrex will be used predominantly by small and mid-size businesses."

Adopting managed IP telephony with IP PBXs managed remotely by service providers is an option for customers who either lack staff expertise in IP voice or otherwise prefer not to use their staff to look after the new technology, said Gartner.

But a key factor in the speed of managed IP telephony success will be service provider pricing, warned Koppman warned.

"Businesses will look for a single, easily understandable price, on a per-seat or similar basis, rather than complex, per-component pricing. Carriers should be able to get deep discounts from equipment vendors, and carriers would do well to pass much of the savings on to buyers," he said.