VoiceXML and the VoiceASP

by Jonathan Eisenzopf

So you want to develop and deploy a VoiceXML application, but you're not sure whether to build your own VoiceXML gateway, buy a turnkey solution, or host your application? This article will lay out the pros and cons when considering a VoiceASP and discuss the features, costs, and tools provided by each of the top vendors.

So you want to develop and deploy a VoiceXML application, but you're not sure whether to build your own VoiceXML gateway, buy a turnkey solution, or host your application? This article will lay out the pros and cons when considering a VoiceASP and discuss the features, costs, and tools provided by each of the top vendors.

A Voice ASP is similar to Web hosting company in that you pay a pre-determined fee that gives you access to their equipment and Internet connection. In the case of VoiceASPs, you typically will pay a setup fee and per-minute usage fee, similar to your long distance service. You are provided with a toll-free or local number that your customers call to access your applications. The VoiceASP handles all of the incoming calls and interacts with the VoiceXML pages and applications on your Web server. To reduce the time it takes for the Voice ASP's gateway to interact with your Web server, you can usually co-locate your server at the same data center that contains the equipment that will be handling your calls. We will be looking at the top three Voice ASP providers: BeVocal, Tellme, and Voxeo.

Voice ASP benefits

Building your own VoiceXML gateway solution is not only complex, it's also expensive. Even if you do have the in-house expertise, building a gateway from scratch will cost at least $10,000 for as few as 4 ports (phone lines). Furthermore, if you experience a fluctuating call volume, you might have to purchase your equipment based on these peaks, which could mean that it only gets fully utilized five percent of the year. Voice ASPs also eliminate the maintenance costs, which usually far exceed the cost of the equipment and software. Furthermore, the three VoiceASPs that we're looking at, Tellme, BeVocal, and Voxeo, include Web-based tools to help you develop and troubleshoot your applications. And add the fact that your out-of-pocket cost to start developing and testing applications with all three ASPs is $0. The benefits of using a VoiceASP become very compelling, but before you sign up, let's look at some of the drawbacks and limitations that you'll have to address when you consider using a Voice ASP.

Voice ASP limitations and drawbacks

When evaluating whether you should use a Voice ASP, you need to consider the drawbacks. Part of your infrastructure might be in another location so this could cause problems if the Internet connection between the provider's gateway and your Web server is interupted at any point. Also, when using an ASP, you are stuck with the functionality that they provide. Each ASP has a different set of features. One might support the latest standards while another lags 6 months behind. Another drawback to using an ASP is the lag that is related to the time it takes the ASP's gateway to perform a transaction with your Web server, which might be on the other side of the country. Depending on the lag at the time, customers might be waiting several seconds before they hear back from the server. Even worse, they might hear nothing. Additionally, if your provider doesn't maintain a low enough utilization rate, your customers might be welcomed by a busy signal because other customers are saturating all of the inbound ports.

What you need to ask

The first thing you need to consider about using a Voice ASP, especially when the application they're hosting is critical to your business, is that you will be depending on a third party whose equipment and staff are out of sight. Make sure that both you and the ASP have an agreed upon quality of service agreement. How long is it ok for customers to not be able to reach the application? If it's critical to your business, it's never ok, so does your ASP have a guarantee of service clause? All of the Voice ASPs are partnered with major telecommunications providers like AT&T, who provide the basic telecommunications infrastructure, but you will still want to get information about utilization rates for their VoiceXML gateways. You don't want customers to ever get a busy signal and you want to be able to scale call volume for promotions or special events. You will also want to ask about outbound call support if you expect that you will ever to need to make outbound calls in addition to inbound calls.


Expect to pay anywhere from $0 to $30,000 to get started with an ASP. The setup fee is based upon your expected usage. Once you're set up, you should expect to pay from thirty to fifty cents per minute for usage. It's billed much in the same way that you pay for regular long distance service, except the cost per minute will be higher. Tellme caters to larger customers, which will probably also charge the highest setup cost and expect you to have a high call volume. Tellme is also the most well established Voice ASP, offering a myriad of options for larger customers. Voxeo, being the smallest of the three, is able to cater to smaller customers.


All three of the Voice ASPs use Nuance software for speech recognition. This means that you will be able to use GSL grammars with any of the providers. Tellme and BeVocal have their own VoiceXML interpreters, which means that there are certain features that may not be well supported or extensions that each has made that isn't part of the standard. Voxeo utilizes the VoiceXML interpreter from Nuance, which means that if you use Nuance development tools, you can be fairly sure that your application will work with Voxeo. As of thus writing, BeVocal is the only ASP that currently supports VoiceXML 2.0. I'm fairly certain that the other will support the new draft of VoiceXML shortly.

Development Tools

BeVocal provides the best set of development tools, though Tellme is a close second. Voxeo does provide a Windows application for building VoiceXML though, which can be helpful if you're aren't online since the others are strictly Web based.


If you are a small to medium sized business, your best bet is Voxeo. If you are a larger company that needs advanced features and good support, Tellme is probably the one. If you want the best tools and best support for new standards and technology, I would select BeVocal. BeVocal has the best developer support in my opinion. Voxeo has a a great VoiceXML-like language called CallXML, which makes it easy to perform advanced call control and place outbound calls. Tellme has good call center and IVR integration. The best thing to do is sign up for all three and test them out.


About Jonathan Eisenzopf

Jonathan is a member of the Ferrum Group, LLC based in Reston, Virginia that specializes in Voice Web consulting and training. He has also written articles for other online and print publications including WebReference.com and WDVL.com. Feel free to send an email to eisen@ferrumgroup.com regarding questions or comments about the VoiceXML Developer series, or for more information about training and consulting services.

This article was originally published on Saturday Sep 28th 2002
Mobile Site | Full Site