Phone applet is downloaded from webserver. Basic phone GUI with standard buttons plus extra loopback drop-down box for troubleshooting. Applet connects back to server via TCP. There is NO SIP or any other signalling, just a 2 dozen XML commands going back and forth to server. Developer must be very familiar with JavaSound, especially with GSM codec, and datagram neworking, must be able to loop microphone to speaker (1) directly, (2) after codec, (3) on datagrams, (4) on server. During the call remote party should be looped as well. Other codec used: uLaw, aLaw, PCM - no RTP at all.