FreePBX is included in open source third party distributions such as FreePBX Distro, AsteriskNOW, Elastix and RasPBX. FreePBX offers some interesting features like Voicemail, Ring Groups, Unlimited number of Conferences, Paging and Intercom functionality, support for Session Initiation Protocol (SIP) phones, Call Queues, support for IAX and ZAP clients, and Asterisk Recording Interface (ARI). FreePBX is developed using Linux, Apache, MySQL, and PHP (LAMP).