Verizon Business is extending many of the functions of a PBX phone system to BlackBerry users through a new offering based on technology from Ascendent Systems, a subsidiary of BlackBerry maker Research In Motion.

The PBX mobile extension product is similar to one that Verizon already offers, but it now requires no dedicated hardware. An enterprise can use server software and a phone client from Ascendent, in addition to their existing PBX, to allow users to set up as many as four phones, including their BlackBerry device, to ring automatically at the same time their desk phones rings.

While the offering works with Symbian and Windows Mobile phones, BlackBerry users will get the most functions when the offering is combined with the BlackBerry Mobile Voice System, said Kelly Brown, group manager, emerging services product marketing at Verizon Business.

In addition to making and receiving calls to their desk phones on their BlackBerry devices, users can access a drop-down menu on their BlackBerry to check their desk phone voicemail box.

Verizon Business planned to announce the new offering at the CTIA show in Las Vegas on Tuesday.

The offering also lets users easily coordinate conference calls from their BlackBerry.

Users can also switch a call from their desktop phone to the BlackBerry in mid-call. From their BlackBerry they can make calls to co-workers by dialling only four digits, and access other PBX functions such as transfer and hold.

A Web-based interface lets users set preferences, such as which phone numbers they would like to ring when calls come in to their desk phone and during which hours of the day. Administrators use a separate tool to define profiles and set restrictions for users.

Enterprises pay a one-time fee for the server. Verizon Business, a group within the operator that sells services to enterprises, will offer the Ascendent platform to enterprises and assist them in setting it up.

The product doesn’t offer all the capabilities of unified communications offerings from Cisco and Microsoft, Brown said. Nor will it compete with future services that might come when operators do more network integration. But the Ascendent software gives enterprises some of the features of those solutions now in an easy-to-use product, she said.