I compiled Signal for iOS and monitored the sent data through a proxy. Both behave identical. There could be a hidden switch in the distributed binaries that triggers other behavior, but I really doubt it. For Android, there are reproducible builds so you can actually check the code is the same. For iOS reproducible builds are harder but should still be possible.
Can I verify that the build installed on my Android phone[] is identical to the one that I compiled? For instance, if I mount the device in Linux I can only see /mnt/sdcard, not /, so I can't copy the binaries off.
[] i.e. the build installed on my phone, not the build available no Google's server to download.
