C&W said the new service would enable firms to send voice calls over IP without replacing existing telecoms equipment.
The service, designed for businesses with 250 or more users across two or more sites, provides an IP converter to allow private branch exchange users to continue running their existing phone networks.
C&W said it could be used by firms with an existing IP virtual private network with quality of service infrastructure. It estimated that firms could make savings of millions of pounds a year by using its existing Wan for voice communications.
Quocirca analyst Clive Longbottom warned users to be wary of the way the service is charged. He said, "You should ensure that calls between two IP-connected companies do not cost anything."