Gianfranco, one of our partners, released a new softphone SDK. This SDK provides full SIP features, such as HOLD, Transfer, and so on. It works as .net component or .com component. It is easy to build a new softphone base on this SDK.

Most important, it has been tested with lots of SIP servers or proxy, such as our SIP server (miniSipServer), Asterisk, OpenSER and so on.

If you are interesting in building your own SIP softphone, this SDK could be a very good choice for you.

The official website is http://www.lullabysdk.com/