In principle, since both the Signal client and server are FLOSS, it should be possible to resist a block in some ways that might not be so easy with for example Whatsapp, but as far as I can tell, as things stand right now there is no built-in way to switch server, and asking millions of regular people to make changes to the source code of their cellphone software, recompile and manually reinstall does not seem like a recipe for success. I wonder if one might sensibly work around these things by fallback/optional connection to the server through Tor if Tor is available on the device?

And I am! I can't wait for Novena! Also notice a difference. Having a close-sourced CPU is different than having a close-source browser which has much more possibilities to compromise you. It can start camera, microphone, read disk files, locate you and transmit everything to "cloud".