Instalar Skype en Ubuntu desde repositorio

Agregar el PPA correspondiente a la versión de Ubuntu que tengas instalada:

Skype for Ubuntu 14.04
sudo sh -c "echo 'deb http://archive.canonical.com/ubuntu/ trusty partner' >> /etc/apt/sources.list.d/canonical_partner.list"

Skype For Ubuntu 13.10
sudo sh -c "echo 'deb http://archive.canonical.com/ubuntu/ saucy partner' >> /etc/apt/sources.list.d/canonical_partner.list"

Skype For Ubuntu 13.04
sudo sh -c "echo 'deb http://archive.canonical.com/ubuntu/ raring partner' >> /etc/apt/sources.list.d/canonical_partner.list"

Skype For Ubuntu 12.10
sudo sh -c "echo 'deb http://archive.canonical.com/ubuntu/ quantal partner' >> /etc/apt/sources.list.d/canonical_partner.list"

Skype For Ubuntu 12.04
sudo sh -c "echo 'deb http://archive.canonical.com/ubuntu/ precise partner' >> /etc/apt/sources.list.d/canonical_partner.list"

Una vez agregado el PPA:

sudo apt-get update
sudo apt-get install skype