Voip phone services
Asterisk phone
http://en.wikipedia.org/wiki/Analog_telephone_adapter
http://www.mikesoares.com/guides/asterisk/\\
===Outside===
http://forums.digium.com/viewtopic.php?p=60983&sid=8519cbb3869300c8c2b58639788f77d1\\
===Certification===
[[http://www.cisco.com/web/learning/le3/le2/le0/le3/learning_certification_type_home.html|CCNA voice]] cerfication by Cisco, [[http://www.amazon.com/CCNA-Voice-Study-Guide-640-460/dp/0470527668/ref=sr_1_1?s=books&ie=UTF8&qid=1311179198&sr=1-1|book]]\\