If using FreePBX on Warp then a FTP server can be added through the FreePBX Addons page as shown in the screenshot below.


Alternatively if FreePBX is not being used a FTP server can be manually added to the unit with the following command.

  apt-get install proftpd
The following link describes more details about the proftpd package under Debian - http://www.debian-administration.org/articles/228