As other DC clients, DeltaTouch v2.220 comes with experimental calls support. To test the new call feature, go to Settings → Advanced, enable “Experimental Features” and then “Debug calls”. You will then see a new button in the header of 1:1 (direct/private) chats, click there to start calling!
NOTE 1: It is a know issue that outgoing video from Ubuntu Touch devices does not work at the moment, and incoming video only works sometimes. Please report if audio is not working though.
NOTE 2: report your experience using different networks etc. did you manage to establish the p2p call or was not possible? tests using mobile data are appreciated, but may consume a lot of data as not yet optimized