Grandstream UCM6304A Audio Series IP PBX

The Grandstream UCM6304A is an on-premise IP PBX for up to 1,000 SIP users and 150 concurrent calls, with four FXS ports, four FXO ports and seven audio conference rooms holding up to 120 parties.

The A means audio only. The non-A UCM6304 adds video meeting hosting; this does not. Since nearly every organisation already runs video on Teams, Zoom or Meet, the A is usually the sensible specification — the same PBX, the same voice features, without paying for a video platform that will sit unused.

At this size the analogue ports are usually about obligations, not preference. Four FXO ports carry four real telephone lines and four FXS ports keep analogue devices alive — which in a building of this scale typically means a lift line, an alarm panel, a fire line and a fax that someone insists still matters. Those are the connections that have to keep working when the internet does not.

Key features

• Up to 1,000 SIP users — extensions registered to the system
• 150 concurrent calls — the figure that actually sizes the platform
• 120 SRTP encrypted calls — note this is lower than the total call figure
• 4 FXO ports — connect four analogue telephone lines
• 4 FXS ports with lifeline — analogue phones and faxes, with dial tone in a failure
• 7 audio conference rooms, up to 120 parties — meetings on your own system
• USB and SD card interfaces — local storage for recordings and backups
• Call recording, IVR, queues and voicemail — the full business feature set
• On-premise — your calls, recordings and data stay on your own hardware

Works with

• Grandstream UCM6302A — 500 users and 2 FXS / 2 FXO ports
• Grandstream UCM6308A — 1,500 users and 8 FXS / 8 FXO ports
• Grandstream HT881 — add eight more analogue lines separately
• Grandstream GRP2604P — a reception phone with BLF keys
• PSU for UCM620x — spare or replacement adapter
• All IP PBX solutions

Frequently asked questions

What does the A actually change?

It removes video meeting hosting. Voice, messaging, audio conferencing, recording, queues and IVR are all still there.

1,000 users or 150 calls — which is the real limit?

The 150 concurrent calls. Users are just registrations; what sizes a PBX is how many people talk at once. A normal office rarely exceeds one call per four or five staff at peak.

Why is the encrypted call figure lower?

Encryption costs processing. The platform handles 150 calls in total but 120 of them encrypted with SRTP. If you intend to encrypt everything, size against 120, not 150.

What are the FXO ports for?

Real analogue telephone lines — typically kept as a fallback for when the internet is down, or because a lift line or alarm line legally has to stay.

What does lifeline on the FXS ports mean?

If power or the network fails, a phone on the FXS port falls through to an analogue line and still gets dial tone.

What happens if the PBX fails?

An on-premise PBX is a single point of failure unless you plan for it. At 1,000 users that is worth designing for — ask us about redundancy before you commit.

Sizing a phone system? Call 0333 242 1314 or email sales@clisecure.com with your headcount, your busiest-hour call volume and any analogue lines you must keep.