POTS in a box: what it is and when it works

Who this page is for

• You have several copper lines ending in the same telecom room or closet.
• Some of those lines serve life-safety devices, and some serve gates, fax machines or card terminals.
• Your carrier sent a notice, or the line prices went up, and you want one device instead of many.
• You want to know what a vendor means by “POTS in a box” before you sign.

The situation this device is built for

A typical mid-rise building has a small telecom closet in the basement. In it, five copper pairs land on a punch-down block: two for the elevator phones, one for the fire alarm panel, one for the gate and one for the leasing office fax.

When the carrier retires copper, each of those pairs needs a new source of dial tone. A POTS in a box gives all five a new source in one place, with one battery and one monitored connection.

What is inside a POTS in a box

Every vendor packages it differently, but the parts are the same:

• Cellular router. An LTE (and on newer units, 5G) modem with external or internal antennas. Most carry two SIM cards so the unit can switch carriers.
• Analog ports (FXS). These produce dial tone and ring voltage, like the phone company’s jack. Your devices plug in with the same cables.
• Wired WAN port. Many units can also use a wired internet connection as a second path.
• Battery. Keeps the unit running when building power fails. It does not power your fax machine or gate operator.
• Managed network. Many vendors route calls over a private carrier network instead of the public internet. The industry term is managed facilities-based voice network (MFVN), defined in the glossary.
• Portal and alerts. A web dashboard that shows signal, battery and line status for each unit.

Here is what five vendors and AT&T publish about their units, as of October 2026:

Device	Analog lines	Cellular	Battery (vendor figure)
Ooma AirDial	4 FXS ports per unit (datasheet)	Cat-4 LTE, dual micro-SIM plus eSIM	16 hours standby; over 24 hours with an optional external battery
Granite EPIK	Up to 8 (Granite)	4G LTE, dual SIM, “prepared for 5G”	Up to 24 hours standby or 8 hours of use
IPFone POTSBOX Pro	2, 4 or 8 port adapters, up to 16 lines (IPFone)	4G/5G LTE, dual SIM active/active	12 to 48 hours
MetTel POTS Transformation	Up to 8 (MetTel)	LTE/5G, dual SIM, multi-carrier	Up to 48 hours
BCN POTS over LTE	Not published (BCN)	LTE, dual SIM	8 hours, 24 hours optional
AT&T Phone - Advanced	Up to six devices (AT&T)	AT&T cellular, with broadband first	24-hour battery backup; does not power connected devices

Dual carrier, dual path and why the wording matters

Vendors use similar words for different designs. Ask which one you are buying.

• Dual SIM. Two SIM cards, usually from two carriers. Many units use one at a time and switch on failure, which can take seconds or minutes.
• Active/active. Both connections stay up at the same time. IPFone describes its dual-SIM option this way.
• Cellular plus wired. Ooma says its MultiPath design sends voice traffic over LTE and wired Ethernet at the same time. That only helps if the building has a wired connection to plug in.
• Two paths for fire alarms. NFPA 72 has its own definition of single and multiple communication paths. Two SIM cards in one box are not automatically “two paths” to the fire marshal. See the fire alarm communicator page.

What works well and what is tricky

Usually works well:

• Elevator emergency phones, once line monitoring and the call destination are set up. See elevator phone lines.
• Gate and door entry boxes that call a phone number and accept a tone to open.
• Emergency call boxes and area of refuge stations. See emergency call boxes.
• Plain voice lines for a front desk or a guard booth.

Needs testing before you cancel copper:

• Alarm formats. Burglar and fire panels send short data bursts (formats such as Contact ID) as tones. Compression, latency and jitter on cellular can corrupt them. Granite says its patented Alarm Protocol Relay is a “latency compensation algorithm” for this problem (Granite). Ask every vendor which formats it has tested with your panel brand.
• Fax. Fax machines negotiate speed with the far end. Over cellular they often need a lower speed or error correction turned on. None of the vendor pages I read lists supported fax speeds, so run a long multi-page test.
• Modems. ATMs, card terminals, elevator monitoring modems and utility meters use dial-up data. Granite and MetTel say they support analog modems. Others may not.
• Line seizure. Alarm panels wired through an RJ31X jack must be able to grab the line from other phones. The installer should keep that wiring intact.
• Signal in the wrong room. Basements, elevator machine rooms and steel shafts block cellular. Most vendors offer an external antenna.

Battery backup: what to expect by use

The box battery keeps the connection alive. The device on the other end needs its own power. Rules differ by system:

Use	What official guidance says	Source
Fire alarm communications equipment	NC’s summary of NFPA 72 (2013): 24 hours of backup for shared on-premises communications equipment; 8 hours allowed with AHJ approval and a risk analysis	NC State Construction Office
Managed voice network equipment for fire alarms	NJ’s 2011 bulletin: 8 hours of standby for premises equipment, 24 hours at the central office	NJ DCA Bulletin 11-2
Elevator emergency communication	NC’s summary of ASME A17.1-2019: auxiliary power with at least 4 hours of backup	NC State Construction Office
Gate, fax, card terminal	No code minimum; set by how long you need them during an outage	Your own policy

Your adopted code edition can differ from these summaries. The fire marshal or elevator inspector confirms the number that applies to you.

Listings and certifications vendors claim

These are each vendor’s own statements. A device listing is not the same as acceptance of your installation.

• Ooma AirDial. Ooma says independent testing firms certified it to UL 864 and UL 62368-1, that the California State Fire Marshal listed it as a cellular communicator for compatible fire alarm control units, and that the New York City Fire Department approved it as an MFVN (Ooma).
• Granite EPIK. Granite says the California State Fire Marshal approved EPIK for listing in 2022 and the FDNY approved it as an MFVN on November 23, 2022 (Granite).
• IPFone POTSBOX Pro. IPFone describes it as “NFPA 72 MFVN-approved” [VERIFICAR].
• MetTel. MetTel describes its solution as UL- and FCC-compliant and shows UL, ETL, CalFire and FDNY logos without listing numbers.
• BCN. BCN says its LTE device is designed for NFPA 72.

Managed monitoring: what the alerts should cover

A line that fails silently is the real risk. Before signing, confirm the portal alerts on:

• Loss of building power and switch to battery
• Low battery
• Loss of cellular signal or a carrier switch
• A port that goes off-hook or stops responding
• Calls to specific numbers, such as 911 (Ooma lists this alert)

Send those alerts to a person or a desk that is staffed, not to a shared inbox nobody reads.

My recommendation by scenario

• If you have 2 to 4 lines in one room: a single 4-port unit is usually enough. Ask the vendor to put the fire alarm on its own port and test it with the monitoring company.
• If lines are spread across floors: you may need more than one unit, or new wiring back to one room. Price both.
• If the building has a wired internet connection: pick a unit that uses it as a second path.
• If your fire alarm company prefers a dedicated communicator: keep the fire panel off the box and use the box for everything else.

Use the POTS cost calculator to compare a per-line quote with your current bill. For the other two approaches (dedicated communicators and VoIP adapters) and the full provider table, see the POTS line replacement guide.

How installation works

1. Line survey. Label each pair and the device it serves.
2. Signal test. Measure LTE signal for each carrier where the unit will be mounted.
3. Install and cross-connect. The installer mounts the box, connects power and moves each pair to a port.
4. System tests. The elevator contractor tests the cab phone; the alarm contractor sends test signals to the monitoring company.
5. Acceptance. Where required, the inspector or fire marshal reviews the change.
6. Cancel copper. Only after every line passes.

A single room with good signal is often a one-visit job. Coordinating two trades and an inspection can stretch it to several weeks.

Questions to ask any POTS in a box vendor

• How many analog ports does one unit have, and what happens when I need more?
• Which alarm formats and panel brands have you tested?
• What fax speeds do you support, and do you use T.38?
• What is the battery runtime on standby and in use?
• Does the unit switch carriers automatically, and how fast?
• Do you own the monitoring, or do I need a separate monitoring contract?
• Can you send the listing or approval document for fire alarm use?

Common mistakes

1. Mounting the box where the old block is, not where the signal is. Move the box, or add an antenna.
2. Assuming the battery runs the devices. It runs the box. The gate operator and fax still need power.
3. Putting every line on one unit without asking the fire marshal. Some jurisdictions want the fire alarm on its own listed path.
4. Skipping the multi-page fax test. One test page passing does not mean a 30-page fax will.
5. Not naming who gets the alerts. An unanswered alert is the same as no alert.

If you want two or three POTS in a box quotes for the same building, send me your line list for a quote.