It would just go over the air as data. For example, 1500 minutes of G729a voice uses (4.12kB/s * 60 seconds * 1500 minutes) = 370 MB
The question is what kind deal Google could cut with the carriers to provide nothing more than 370MB a month of data transit.
Because the package management system runs as root, may install setuid files, or system daemons which contain vulnerable code; an unprivileged user cannot normally do this.
Sure - only signed packages can be installed - but signing a package won't make those pesky buffer overflow vulnerabilities go away.
Trying to be happy is like trying to build a machine for which the only specification is that it should run noiselessly.