For decades, telecommunications software has been developed by voice-system vendors and tightly integrated with the hardware they sell for PBXs and call centers. But the growing adoption of voice over IP, where voice calls run over a data network like any other application, has the potential to uncouple the proprietary hardware-software link and open up telecom software development to more third parties.

The telecom industry expects great benefits from combining VoIP with emerging standards, such as VoiceXML and the Session Initiation Protocol, that allow for easier development, interoperability among systems, and application integration, along with open APIs that vendors are adding to their products. "The promise is that a fairly well-trained high school grad can write a VoiceXML app," says Barry O'Sullivan, VP and general manager of the IP communications business unit at Cisco Systems.

That would be a big change for an industry that relies on proprietary systems to keep customers paying for upgrades and new features. The VoIP and open-standards combo should produce more choices and lower prices. "Open standards is the key," says Lawrence Byrd, a director in the enterprise communications applications division of Avaya Inc., a supplier of business-communications systems.

	A Linux-based PBX eases app development, Yarde Metals CTO Pippenger says.

Telecom software development is wrought with challenges. Applications must work with cell phones, PDAs, office phones, PBXs, and call centers and operate across a range of wired and wireless networks from different service providers. They also need to scale to millions of users. While those challenges won't go away, VoIP makes it easier to tackle them.

Systems vendors and service providers plan to use VoIP to create unified communications systems that integrate voice calls, voice mail, E-mail, instant messaging, and conferencing. VoIP makes it easier to retrieve a voice message from a PC or have E-mail read over a phone. Such apps exist now, but they'll become more integrated and easier to use over the next couple of years, vendors say.

Another goal is to voice-enable more applications so users can access features, find information, and route messages using simple voice commands. The ease of rerouting VoIP calls makes it easier to provision remote workers, letting them answer calls from home and appear as if they're in a call center.

VoIP also may boost open-source software, which costs little or nothing and can be modified by the user. Yarde Metals Inc., a distributor of specialized metal products, this year began deploying the Asterisk open-source PBX, a voice-communications system that runs on a PC running Linux. While Asterisk doesn't have as full a feature set as many proprietary products, it's easy for Yarde to write some apps. "Everything that happens in the PBX is posted to a SQL database," chief technology officer Dave Pippenger says. "The configuration is done in Unix text files. It's easy to roll your own PBX."

Writing voice applications may never be as common as writing computer apps. But the spread of VoIP will make it easier to manage applications and add capabilities to the voice feature set. In a decade, the telecom network "will be like getting water out of the tap," predicts Stef van Aarle, VP of marketing and strategy at Lucent Worldwide Services. "The only time you think of it will be when it doesn't work. And software is the glue that makes it all easy to use."