Earlier quoted context omitted.
Can I download the the Signal client from any store and then point it to my own server instead of Whisper's? Did anybody try to run his own server? Can such setup really work?
You can run your own server, but there's no federation. 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?