Asterisk has a number of optional build dependencies.  If you intend to
use any analogue PSTN hardware such as DigiumTDM400P, you should install
the dahdi-linux and dahdi-tools software and drivers before compiling
Asterisk.  If you will instead use digital telephony hardware (not IP
phones) such as T1/E1 lines or a PRI, you'll need to install libpri,
again before compiling Asterisk.

Be sure to see /usr/doc/asterisk-1.6.1.6/sample_confs/ after installation
for any additional configuration files you may need.

Note that dahdi-linux and dahdi-tools are currently not available in
our repository due to broken download links; we hope that will be
resolved soonish.