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.