Ozeki VoIP SIP .NET SDK allows to develop Do Not Disturb (DND) function for SIP softphones. If DoNotDisturb flag is set to true, the incoming calls will be rejected by a busy signal. The Ozeki VoIP SIP SDK makes it possible to extend this program with more features like call hold, call forwarding, call transfer, auto answer, SIP/SDP message manipulation, .mp3 and .wav playing support, etc. The softphone is customizable with your own company name. The Do Not Disturb functionality is really simple to handle when you use Ozeki VoIP SIP SDK. DND indication can be implemented in more ways. Either the client of the caller can show the presence information of the contacts or the DND can be only showed by sending an auto answer message about the fact that the caller does not want an incoming call. The DoNotDisturb is a simple flag related to the phone line. The SDK provides all the background for the DND function. If you set the DoNotDisturb flag to true, the incoming calls will be rejected by a busy signal. The easiest way for extending your softphone with DND functionality is to use a simple checkbox, that indicates if you want to get incoming calls or not. Since the Do Not Disturb function is indicated by the checked state of the new checkbox on the GUI, a new event handler method is required that notifies about the check changes. The method sets the DoNotDisturb property of the phone line according to the check state of the checkbox, if there is a valid phone line. In the case if there are no phone lines, the method does nothing. Ozeki SIP SDK offers various products and possibilities: Softphone, VoIP client applications: Dialers, Call assistant, Call center clients, Call center servers, PBX systems, IVR systems, Webphone solutions, Conferencing systems, Voice recording systems, VoIP tunneling systems, Security monitoring systems, Mobile communication systems. Royalty free licensing is also ensured and a purchased Ozeki SDK license can be used for as long as you wish