We are looking for a custom-built SIP Softphone (PJSip Asterisk extensions) project using .Net 5 and C# to with the following features:
1) Source Code in Visual Studio project using .Net 5 for Windows Application
2) Downloadable internal directory/contacts
3) Simple UI
4) Minimizable to Tray
5) DTMF and Multi-line with hold, conference, transfer
6) Configurable ring notifications
7) Cannot use proprietary/paid license components
8) Completely configurable from web endpoint (can be XML/YAML/text for the extension, server, etc)
9) Code standardly documented in English