Only Blackberry offers voice security, either through Blackberry Enterprise server or with a Secusmart chip at both ends. Blackberry bought Secusmart last month. Angela Merkel uses A Blackberry Q10 smartphone with a Secusmart chip to avoid NSA snooping of her voice communications.
Actually, Apple does, if you use FaceTime voice or visually. It is 128 bit encrypted and Apple does not archive anything, nor can they decrypt the messages being transferred between you and the recipient. Also, iMessage is encrypted the same way. . . and also not archived. They can only be eavesdropped on the old fashioned way. . . someone hanging from the eaves and listening.
Otherwise, you are correct. The voice over cellular is dependent on the security of the carrier. . . as is the messaging.