XO Communications is moving its Voice over IP service up market, adding PBX support to attract and serve larger enterprise customers.

The enhancements to XOptionsFlex will enable businesses with up to 160 employees at an individual site to use VoIP with an existing key system or PBX by offering PRI and digital trunk support.

“We are seeing more demand from higher-end customers and our first launch wasn’t able to meet that demand,” said Nicola Jackson, director of product management for XO. “This will help us move up market to serve higher end customers.”

Initially, XO is supporting Avaya PBXs, but it is well under way in interoperability tests with other PBX vendors, Jackson said. The service will be available immediately in Minneapolis, Chicago, Dallas, San Francisco and the Florida cities of Miami, Ft. Lauderdale, Tampa and Orlando. It will be available nationally within the first half of the year.

“One of the key things that we uncovered was the absolute need to insure interoperability between our network and customer’s PBX,” Jackson said. “The underlying signaling is SIP, but each implementation is a little different. We did a tremendous amount of work in our labs to insure interoperability between our product and our networks and certain PBXs.”

The company has a rollout schedule for future PBX interoperability, she said.

XO has signed 3000 customers to its XOptionsFlex since its launch in 2005, and the number of multi-site customers has exceeded expectations, Jackson said.

While smaller businesses have initially been drawn to the service for its cost savings, they are beginning to discover productivity benefits as well, she added. “That’s what creates the stickiness,” Jackson said.