Short answer
Yes. Hybrid set-ups are common: FirstNet SIP Trunks stay under your existing PBX while selected users move to Zoom Phone, with dial plans and emergency routing aligned across both.
In detail
How a hybrid design is scoped:
- Decide which users move to Zoom Phone and which stay on the PBX.
- Keep the PBX on FirstNet SIP Trunks, so both platforms run on FirstNet's ICASA-licensed network.
- Align dial plans so users on either platform can reach each other.
- Align emergency routing so emergency calls work correctly from both platforms.
- Plan which numbers stay with the PBX and which move to Zoom.
This works with PBXs such as Yeastar as well as other SIP-compliant systems. Users who stay on the PBX can move later in waves without changing the voice provider underneath.
FirstNet's voice engineers scope the boundary between the two platforms, how the SIP underlay is shared and the porting plan. A pilot group goes live on Zoom Phone first, with hyper-care during cutover, and the remaining users follow once the pilot is accepted. Legacy carrier traffic is then retired on a documented date, so nothing is left running by accident.
Source: FirstNet Zoom Phone & Zoom Contact Centre service page →
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