ASP.NET VoIP programming

Your task is to create VoIP feature in ASP.NET for our website application. This will be done using one of three pre-coded sets of VoIP routines (SDKs). We will choose the SDK together. The first goal is to be able to send an automatic voice message to the recepient, similar to reading an SMS. Later, you may be asked to add more features, such as VoIP voice calling, answering machine, voice mail and similar. The chosen programmer will receive more details about the project. When bidding please supply references to similar projects you have done in the past.