Hamvoip is based on Arch not Debian! So you need to use the correct package manager.

pacman -Sy package_name

This will install packages in Arch, if you need further information about pacman (not the arcade game!) then type...

man pacman

This will print out the manual to screen so that you can read it.

Apt is Debian's package management as yum is for redhat/fedora based systems.

Cheers