Enormous APP could be installed in cell phone. Also, cell phone’s OS would be modified by multiple vendors. Malicious and improper authorization applications might exit in cell phone. Voice of ell phone call or APP call might be captured.
All the voice signal will be handled by Telecom or APP server. Those server might capture your voice signal without your intention. Encrypt your voice before transferring into Telecom or APP server is important.
The connection between cell phone and base station is wirelessly. The electric wave is broadcasted widely. With special instrument, these electric wave could be captured. Although protocol of these electric wave contain encryption feature. There are many well known software/device to retrieve the original signal. Without other protection/encryption, your information is spread wirelessly and widely.
Cell phone must connect to base station to work. Or, cell phone can’t send/receive information. Base station control cell phone’s data transference. When cell phone connect to malicious base station, the data transference could be controlled by unknown organization.