Here is a sample VoIP API call, which as you will notice uses XML:
<?xml version="1.0" encoding="UTF-8"?>
This use of XML as the VoIP API reminds me that Microsoft Live Meeting 2007, Microsoft's collaborative online meeting application featuring VoIP and videoconferencing also leverages XML to allow you to schedule meetings, manager users, and perform reporting functionality. The APIs actually look quite similar come to think of it. They use similar XML calls to create a conference. I'd include a screenshot of a sample Microsoft API call, but I'm under NDA. If you can't wait, you can join the Live Meeting 8 (LM8) beta located here. XML is a beautiful and simplistic method of integrating disparate applications by providing a common language for intercommunication. In fact, SIP and XML are a great combination and are often used together for many VoIP solutions.
In any event, Erik also emailed me and stated, ""Until now the only way developers could integrate scalable and reliable telephony was through acquisition of expensive equipment and infrastructure. Lypp has removed those barriers by building a simple API and allowing our customers to leverage our access to the North American PSTN (Public Switched Telephone Network) including but not limited to TELUS, Rogers, Bell, Verizon, AT&T, Sprint, SBC and BellSouth, through the most trusted interconnect providers in the business including Level 3, Global Crossing and XO."
The Lypp API enables rapid VoIP feature implementation, including: Click-to-Call and Click-to-Conference, virtual phone booth calling features, and integration of basic and advanced telephony such as embedded email and profile call links for FaceBook, MySpace and other web-based applications and services.
The Lypp API is available online at http://lypp.com/api.