The questions have been there for years: Why not send a text message to your airline rather than waiting on hold for an hour? Why can’t my customer information be passed up the call chain with the same ease as my voice? Where are all the cool VoIP applications?

VoIP (voice over IP) has been a buzzword since the turn of the millennium. Now, through the rise of the cloud, VoIP is entering the era of the API. Companies like 2600hz, One Source Networks and Twilio are breaking down the barriers between enterprise phone systems and enterprise applications.

Jeff Lawson, founder and CEO of Twilio, said that VoIP hasn’t been a first-class Web citizen until recently. “It’s not something that was accessible to most developers. It was esoteric and in a totally different realm of programming and technology. Telecom is nothing new, but making it accessible to those Web developers is,” he said.

To that end, Twilio built its cloud-based VoIP APIs with the intention of making the services useful and comprehensible to Web developers. And that, said Lawson, is the key to spreading VoIP integrations.

“We’ve always been about the Web developer,” he said. “It’s the perspective we came from. Before Twilio, I was not in telecom; I was in Web development. We wanted to make these technologies first-class citizens of the Internet. We offer RESTful APIs, and it’s Web technology: HTTP, XML, and you can use it with PHP, Python, or other popular Web languages.”

Gina Nomellini, chief marketing officer at One Source Networks, said that APIs have become the lifeblood of VoIP. “[One Source] sees a number of API interface requirements from its enterprise customer base,” she said. “Our clients have requested to interface with APIs from our hosted VoIP services to Salesforce automation tools such as and Microsoft Dynamics, as well as integration with [Microsoft] Outlook.”

For many companies, adding VoIP integrations to enterprise applications can offer a more diverse way for employees to interact with one another and with customers, said Nomellini. “By leveraging this technology, enterprises achieve flexibility and cost savings, as well as the feature-rich services that a VoIP platform enables,” she said.

“VoIP provides companies with the ability for increased collaboration. It integrates an employee’s entire workstation from their computer to the telephone, allowing them to be more efficient and increase productivity. Today’s VoIP solutions leverage a user’s e-mail, chat features, voice, messaging and video capabilities to provide a holistic service that enhances an enterprise’s ability to respond to its customers more efficiently.”

Of course, the actual usefulness of VoIP depends on the additional capabilities it can bring to an application. One of the primary benefits that Nomellini highlighted is that VoIP can be used to enable workers to do their jobs from just about anywhere. “The enterprise now has the ability to become entirely mobile. This is of benefit for traveling executives that are now able to have a single telephone number and calling instance wherever they are working, around the world,” she said.

“Enterprise call centers also become far more productive as VoIP enables the call-center workers to be physically remote and still productive. The enterprise’s ability to recruit from a wider resource pool provides a better quality workforce all around. Moreover, without the expense of offices, companies pay less overhead on facilities power and real estate inclusive. Finally, with enhanced integration capabilities between fixed and mobile communication services, workforce accessibility is increased.”

But integrations with VoIP systems aren’t entirely about APIs and cloud-based services; they’re also about open-source software. For years, the standard in open-source VoIP was Asterisk. This open-source private branch exchange became quite popular, but it eventually butted up against some platform limitations. Patrick Sullivan, cofounder and COO of 2600hz, said that this is why his company is based on FreeSWITCH, another open-source telephony platform.

“FreeSWITCH started because one of the main developers of Asterisk realized there were some issues in the core of Asterisk,” he said. “The guys at Asterisk were like, ‘We don’t want to scrap this and start over.’ So Anthony Minessale started FreeSWITCH. He focused on it being the core for a scaling solution.

“Instead of supporting only 50 people on a box, he wanted to go much larger. FreeSWITCH quickly took off. You can go with Asterisk, which has bells and whistles, or you can go with FreeSWITCH, which is more scalable.”

FreeSWITCH offers even more potential for application integrations because it is an open-source project. For developers working with VoIP and who understand Erlang, FreeSWITCH offers a carrier-grade VoIP server that can be modified to handle just about anything.

Sullivan’s company, 2600hz, is named after the tone used by phreaks (phone hackers) in the 1970s and 1980s to seize control of phone switching trunks and allow the placement of free phone calls. Ironically, this is the promise of VoIP: free phone calls. But with open-source servers like FreeSWITCH and cloud-based APIs like Twilio’s, VoIP has grown up to become a first-class citizen of the Web. Now it’s just up to developers to discover new and interesting ideas for integrations.