Short description of SIP DLL 1.1: SIP DLL - A powerful and highly versatile VoIP SDK to accelerate development of SIP applications. Our brand-new SIP SDK provides a powerful and highly versatile solution to add quickly SIP (Session Initiation Protocol) based dial and receive phone calls features in your software applications. It accelerates the development of SIP/ RTP compliant soft phone with a fully-customizable user interface and brand name.