Grandstream UCM6308 IP PBX

The Grandstream UCM6308 is the largest on-site PBX in the UCM6300 range: up to 3,000 users and 450 concurrent calls, with eight FXS and eight FXO ports built in. It is the model for organisations that would otherwise need several smaller systems stitched together.

Eight analogue ports of each kind removes the usual reason for a separate gateway. Lift phones, alarm diallers, fax machines, door entry panels and a handful of exchange lines all land directly on the PBX, with lifeline so the analogue side survives a power cut.

If you encrypt call media, plan against the honest number: 450 calls in the clear, 300 with SRTP.

Key features

• Up to 3,000 users — registered SIP endpoints
• 450 concurrent calls, or 300 with SRTP encryption
• 8 FXS and 8 FXO ports — eight analogue devices and eight analogue lines
• Lifeline on the analogue ports — an analogue phone still works in a power cut
• Gigabit networking — router or switch mode
• Full PBX features — voicemail, IVR, call queues, ring groups, call recording
• Wave app — desktop, mobile and web softphone included
• Video and audio meetings — hosted on the PBX itself
• Expandable with gateways — add analogue capacity with a GXW or HT gateway
• No per-seat licence for core telephony

Works with

• UCM6301 — 500 users, 75 calls, 1 FXS + 1 FXO
• UCM6302 — 1000 users, 150 calls, 2 FXS + 2 FXO
• UCM6304 — 2000 users, 300 calls, 4 FXS + 4 FXO
• Grandstream GRP desk phones — zero-touch provisioning from the UCM
• Grandstream DECT cordless — register handsets to the same system
• GXW4248 V2 — add 48 analogue extensions

Frequently asked questions

3,000 users but 450 calls — which number matters?

Concurrent calls, almost always. Size on the busiest ten minutes of your week rather than on headcount.

Why does SRTP reduce the call count?

Encrypting and decrypting media in real time takes processing power, so the ceiling drops from 450 to 300. If everything is encrypted end to end, plan against 300.

What is the difference between FXS and FXO?

FXO takes a line in — plug an analogue exchange line into it. FXS gives a line out — plug an analogue phone, fax or door phone into it. The UCM6308 has eight of each.

One UCM6308 or two UCM6304s?

One box is simpler to run and keeps every extension in one dial plan. Two make sense when you want the estate split across two sites or two failure domains — UCMs can be peered so extensions still reach each other.

Do I still need a SIP provider?

Yes — the UCM is the phone system, not the phone lines. It connects to your SIP trunk provider, or to analogue lines through the FXO ports, or both.

Is there a licence cost?

Not for core telephony — users, calls, voicemail, IVR and queues are included. Optional extras such as UCM Remote Connect for VPN-free remote working are separate subscriptions.

Sizing a phone system? Call 0333 242 1314 or email sales@clisecure.com — tell us the staff count, the busiest hour and how many analogue devices there are, and we will size it properly.