The error seems to come from some external dependency to a package in install_prereq
sh contrib/scripts/install_prereq install
...
Setting up libvpb1 (4.2.59-2) ...
debconf: unable to initialize frontend: Dialog
debconf: (TERM is not set, so the dialog frontend is not usable.)
debconf: falling back to frontend: Readline
Configuring libvpb1
-------------------
This is the numeric code for the region your phone system will be operating in
(eg. 61 for Australia or 33 for France). It is used to configure the default
regional standards that Voicetronix telephony hardware should comply with.
ITU-T telephone code: