I’ve been covering the VoIP space since 2004, and lately it seems like every other press release sent my way is from a company announcing the addition of an application programming interface (API) to its telephony platform. The promise of APIs is that they make it easy to integrate different services — even those provided by different vendors — into a single application. The press release from one carrier even went so far as to claim that its API would “boost innovation and development of new apps exponentially.”

But is simply providing an API to your telephony infrastructure enough to prompt the world to beat a path to your door? Don’t count on it.

To be sure, these APIs are necessary, particularly in the world of voice mashups. Voice mashups combine voice as well as data and applications across multiple systems to create a new, useful service.

One example of a voice mashup is Twitterfone, a free service that takes your voice, converts it to text and sends it to Twitter. MAXroam provides the overall infrastructure and inbound telephone numbers, Dial2Do does the speech-to-text part, and Zong provides some inbound SIP termination. APIs are needed all around — including on the voice side — to make this happen seamlessly.

Voice mashups can be useful in the business space. They can save a ton of money, and can help to enforce both business process quality and consistency. Imagine calling an airline and speaking to an interactive voice response (IVR) system. A certain percentage of calls could easily be handled by the IVR, which can ask all the correct questions to ensure customers have the right information.

There are, of course, times when speaking with a live human being is necessary. So imagine that all the data collected by the IVR about your call is then sent to a customer service representative so that by the time the two of you are connected, they already know exactly why you’re calling. The call could even be routed to a particular rep based on the reason you’re calling.

This is the power of a voice mashup — the ability to treat voice and data interchangeably. While large companies have been able to afford the cost of developing these custom voice mashups, tools and services are now becoming available that let you make your own.

Jaduka started out by providing a voice API to their telephony infrastructure, which is maintained by their parent company, NetworkIP. But Jaduka quickly discovered that while developers signed up for the API, few were actually using it to launch services. The company now offers customized voice-enabled applications to enterprise customers.

Jaduka’s customers currently use over 4 million minutes a month, a number that is trending upward. But that’s a drop in the bucket compared to the more than half a billion minutes a month their parent company serves.

Ifbyphone provides a number of voice-related small business services as well. They also offer a voice API, but it’s essentially driven by web forms, which makes it easy to integrate their telephony services into any web site without needing to be a programmer.

And while not everyone agrees that what Ifbyphone provides would qualify as a proper API, it does offer a range of useful services to small businesses, such as interactive voice response, intelligent call routing and voice broadcast. They are all designed to help small businesses interact directly with their customers in the most efficient manner possible.

Indeed, APIs enable some great solutions. But APIs aren’t solutions in and of themselves. Nor do they necessarily make money.

Consider Ribbit, a company whose business model is to make telephony available through APIs. The thinking is that they’ll make their money on revenue shares as developers create interesting applications.

If Jaduka’s experience is any indication, however, I don’t expect Ribbit will last too much longer without a complete change of strategy. Ribbit might have 4,000 developers, but how many of them are actually making applications on which Ribbit is able to share revenue? I don’t put a lot of stock in the rumor that BT has purchased Ribbit for $55 million.

Even where you’ve got more than just an API, such as the case with Jaduka and Ifbyphone, the prospects for making a pot of money just don’t seem that great. The combined revenue of Jaduka and parent company NetworkIP is thought to be north of $150 million a year. Assuming Jaduka’s share of minutes per month also translates into share of revenue, that suggests Jaduka is responsible for $1.2 million of the revenue. Ifbyphone would not disclose customer numbers or revenues.

I think the market has a lot of potential, but so far, that’s about it. Go ahead and make those telephony APIs available, but don’t expect the world to beat a path to your door, and don’t expect to make any money just by publishing APIs. Figure out who your customers are, find out what problems they have, and develop solutions to meet their needs. APIs can certainly be a part of the overall strategy, but relying on APIs alone to generate revenue is a pipe dream.