A cellular network is allowed to carry packets. It is not allowed to be the place where a conversation becomes readable, and it is not used as the identity of the person holding the phone.
The path
- TunnelApplication traffic is placed on Tor or on a zero-log VPN before it leaves the handset in a form an observer can use. The tunnel is the default path, not an option buried in a settings tree.
- SignalingSIP setup uses TLS 1.3. Call setup, numbers, and session negotiation are not readable to the network that carries them.
- MediaVoice uses SRTP. The carrier transports ciphertext. It does not transport a clear audio channel.
- BasebandThe cellular modem is treated as a separate, hostile computer. It is not given the user’s identity, and it is not the component that terminates the encrypted session.
What an observer still learns
A radio that is powered can be observed. An IMSI catcher can learn that a handset is in range if a SIM is inserted and the cellular radio is on. Timing and volume of traffic can still exist. What the observer does not get from the Theta path is the content of the call, the SIP signaling, or a vendor account tied to the hardware. If presence itself must not be observable, the cellular radio stays off. That rule is in the radios article.
Theta does not record calls. The voice service is a path. It is not a logging system.