When I tried to run
~$ ubuntu-device-flash --server="http://neon.plasma-phone.org" touch --channel="neon-mobile/devel" --bootstrap --developer-mode --password 1234
I got the response:
no --adb-keys defined, using default ~/.android/adbkey.pub
WARNING --developer-mode and --password are dangerous as they remove security features from your device
Get http://neon.plasma-phone.org/channels.json: dial tcp 54.252.125.1:80: i/o timeout

54.252.125.1 didn't respond to ping, but I hadn't assumed that it would.
However, running ...
~$ tcpcheck 10 neon.plasma-phone.org:80
... shows port 80 to be unresponsive.

(In contrast ...
~$ tcpcheck 10 plasma-phone.org:80
plasma-phone.org:80 is alive
... shows the response I would have expected.)

Therefore I assume the reason for the timeout is that the server is inaccessible. Will this be restored soon? If not, is there an alternative URL I can use?