Telephone encoding for broadcast

We are looking for a solution that would allow us to call a service which would encode the voice and send it to a media server. From there, a media player on our Web site will connect to the service allowing for real-time one-to-many broadcast. This will be done in conjunction with a slide show using another product.

We are currently encoding voice for this system, but it requires the presenter’s machine to have a microphone and encoding software. We’d rather just have the presenter call a service to do the encoding and serving.

Does anyone know how we might go about doing this?