Finally, I found time to do some tcpdumps on different OSs for an Xperia X, the result is the following:
1- Ubuntu touch. Fresh install, I left the phone idle without running any apps.
Capturing 1 hour of tcpdump was enough. It’s connecting every several minutes to some canonical and ubports servers. I didn’t dig into what processes were doing this, but this is kind of unacceptable from the privacy/security perspective. I think that this behavior could be tuned by adjusting the services but I did not spent anytime on this.
2- Android 8.1 from vendor. Same condition: fresh install, I left the phone idle without running any apps.
This time, capturing 1 minute was enough, hahha. It’s connecting everywhere
3- Sailfish OS X. Same condition: fresh install, I left the phone idle without running any apps
As soon as it’s connected to internet, it connects to some NTP servers, to ipv4.jolla.com and to some aws server. Exchanges few bytes and stops. It repeats the same process after ~12 hours. It seems some type of network clock synchronization, but I’m not sure.
4- Sailfish OS X. Same as before, but I changed the /etc/connman/main.conf. I removed all the FallbackTimeservers, Ipv4StatusUrl and Ipv6StatusUrl configuration.
It does not connect to anywhere, the tcpdump is totally clean. To me, it’s really unbelievable to see a smartphone network connection complete clean.