Maybe I misunderstood Kontalk's XMPP capabilities: I thought it could work as XMPP client and I would be able to talk with other XMPP contacts outside the Kontalk network.
EVAnaRkISTO at 2015-01-23T23:06:36Z
“I installed Kontalk legacy and it just works like 3.x beta version: It doesn't show 2.x contacts and if I invite them it sends a message directing them to Google Play, which has 2.x version.”
Replicant had flagged privacy on Kontak legacy so it couldn't access any of my contacts. I flagged it off and it can access 2.x contacts now.