I have two thoughts regarding Signal app's requirement of SIM card number for registration.
- It will be no secret for your ISP and/or telecom provider that you are using Signal (unless you are using VPN and you don't use unsecured communication). They will never know anything else (such as who you are talking with, and what you are talking about [and when]).
- You can use a burner phone for registration (if such phones are available in your country). Just get a verification code from Signal using the SIM card number of the burner phone at a public place away from your residence or workplace, then dispose of the burner phone (if you need/want to). Alternatively, you may use a burner number (without the corresponding phone), but you have to trust its provider.
@ash
I hope you were able to read this. Maybe Signal is not for you because of the KYC, but for other people, Signal is very helpful (even for Edward Snowden).
I understand your opinion about giving away your mobile number. Even I at first was not inclined to give my mobile number to Signal due to privacy concerns, but then your ISP will always be able to tell whenever you are using Signal (unless you use VPN). It is pretty much a given that your ISP (and/or telecom provider) will very likely be able to tell that you are using VPN or Tor, and why not just add Signal to the list?