To make and answer phone calls with TSipClient Delphi component you will need an account from a SIP provider like VOIP BUSTER, NET-VOICE, OVH Telecom, SIPNET etc. or you can install PBX like Asterisk on your computer...
The source code of the component is compatible with all Delphi versions starting from Delphi 5 to latest Delphi 12.