Asterisk is an open-source PBX framework that runs on Linux and supports voice calls, IVR, call queues, voicemail, call recording, and SIP trunk connectivity. Since it has no per-seat or per-channel licence fees, it offers significantly lower ownership costs than commercial PBX platforms, especially for businesses with many extensions or concurrent calls. However, it requires skilled Linux and telephony expertise to deploy and maintain.

Raw Asterisk is managed through configuration files and requires Asterisk CLI expertise. FreePBX is a web-based GUI that lets administrators manage extensions, queues, IVR, voicemail, and other PBX features through a browser. FreePBX suits standard office deployments, while raw Asterisk is better for advanced customisation, CRM integration, predictive dialling, and complex IVR workflows.

Asterisk connects to Indian SIP trunk providers using the res_pjsip or legacy chan_sip modules. Common issues include codec mismatches, NAT traversal, DTMF signalling, caller ID formatting, and SIP registration intervals. Experienced Asterisk providers understand these carrier-specific requirements and configure them correctly to ensure reliable connectivity.

Toll fraud occurs when attackers exploit an unsecured Asterisk system to place unauthorized calls, often to premium international numbers, resulting in substantial losses. Key protections include strong SIP authentication, IP whitelisting, fail2ban, restricted AMI access, and outbound call rate limits. These security controls are essential for every production deployment.

AGI (Asterisk Gateway Interface) runs external scripts during calls for tasks like CRM lookups, database queries, and dynamic TTS. ARI (Asterisk REST Interface) provides real-time programmatic control over calls for advanced applications such as custom contact centres, softphones, and IVRs. Businesses typically require AGI or ARI for live data integration, regional language TTS, custom queue logic, or CRM integrations.

On-premise Asterisk offers full control but requires dedicated hardware, IT management, and power backup. Cloud deployments on Indian infrastructure provide easier scaling, automated backups, and high availability. For businesses subject to DPDP Act or RBI requirements, Indian cloud regions are recommended for compliant call recording storage and improved reliability.