Multi-Tenant Hosted PBX Platform

Organizations building a hosted PBX or UCaaS-style product for multiple end-customer businesses face a choice: license a rigid, per-seat SaaS PBX platform with limited customization and vendor lock-in, or build custom multi-tenant infrastructure that can be shaped to the product's specific billing, provisioning, and integration needs. Off-the-shelf SaaS PBX platforms typically become expensive quickly once tenant count grows past a few dozen organizations, and they rarely expose the low-level SIP control needed for custom IVR logic, carrier failover, or white-label branding.

CelloIP is repeatedly engaged by companies in exactly this position: they have identified hosted PBX as a product opportunity but need the underlying multi-tenant telephony infrastructure built from open-source components they can own and operate long-term, rather than rent from a SaaS vendor.

The typical architecture pattern CelloIP builds for this class of project uses FreeSWITCH as the core softswitch, paired with FusionPBX as the multi-tenant management layer — FusionPBX was purpose-built for exactly this use case and provides per-tenant domain isolation, self-service extension management, and a GUI that can be white-labeled per reseller.

At the network edge, a Kamailio or OpenSIPS SBC handles SIP trunk termination, TLS/SRTP enforcement, and carrier failover before traffic reaches the FreeSWITCH cluster — keeping the softswitch layer insulated from malformed or malicious traffic arriving on the public internet-facing trunk.

Billing and CDR processing runs as a separate service consuming FreeSWITCH's CDR events in near-real-time, enabling prepaid balance checks, postpaid invoicing, and per-tenant rate plans — the billing layer is typically the most customized part of the system, since generic SaaS PBX platforms rarely support the specific rating and reseller-margin logic a hosted PBX business needs.