>Why isn't it a walled garden then?
Because the client and server are both OSS?
Because the client and server are both OSS?
Did anybody try to run his own server? Can such setup really work?
The reason for that I imagine is that they want a privacy preserving automatic lookup method (a single server can confirm phone numbers and allow privacy preserving contact list comparisons for its own clients), and aren't convinced of using a model where the public key is the identifier instead of your phone number.
Does the voice communication work?
I'm asking all this because it seems that the server code was earlier in "you can look but it's not enough to run it" state?
There used to be some documentation about running it, but it was removed from the repo (presumably because they didn't want to dedicate resources to supporting it, but that's just a guess).