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.
Apple made this claim of end-to-end voice encryption of FaceTime Audio in a June 16, 2013 press release. Google now makes the same claim about Hangouts. There is skepticism in the hacker community. Any Linux-based OS, such as iOS and Android, can be hacked. Not so with Blackberry OS 10, which was develooed by engineers from QNX, which Blackberry acquired in 2010. Also, Facetime Audio voice quality is dreadful.
You don't see the White House or Angela Merkel using these applications for voice mobile communications. The former uses Blackberry BES and the latter uses Blackberry Secusmart.