Wow. This thread is pretty amazing. My defaulted TDA-50 has a 4-port DHLC. If I plug a digital phone in port 4, it is extension 104. I can dial 204 and get a ringback tone. I can dial 801 on the intercom and get CO line 1.

As I previously said, if you can dial 204 from the digital phone in 104 and hear the ringing, then you have a wiring issue. The quickest way to test calling between 104 and 204 is to use a standard "T" (267A) adapter plugged into port 4. You plug the digital phone on one side and the analog phone on the other.

The drip of information is overwhelming.