Since February 16, 2020, federal rules have required that anyone on a multi-line office phone system can dial 911 without dialing 9 first, and that someone on-site or off-site gets notified the instant that call goes out. That single requirement, known as Kari’s Law, quietly disqualifies a fair number of the phone setups still running in older NYC and NJ offices, and most office managers we talk to have never heard of it.
What a Key System Actually Is
A key system, or KSU, is the setup you’ve probably used without knowing its name: a small box controls a handful of outside lines, and each desk phone has buttons that light up to show which line is in use. It’s simple, it’s cheap to install, and it works fine for an office running a few dozen employees or fewer on straightforward calls. It doesn’t do much beyond that. There’s no real call routing logic, no easy way to add features, and expanding past its line capacity usually means replacing the whole unit rather than adding to it.
What a PBX Actually Is
A PBX is a step up in both capability and complexity — it’s essentially a private phone company sitting inside your building, routing calls between internal extensions and a shared pool of outside lines. That’s what lets a 200-person office run on far fewer outside lines than employees, and it’s what makes features like auto-attendants, voicemail, and call forwarding between departments possible. A PBX scales to hundreds of extensions, but it comes with real hardware sitting in a closet somewhere, and growing it usually means a technician adding capacity, not just buying another phone.
Where VoIP Changes the Math
VoIP moves the phone system off dedicated phone lines and onto your existing internet connection. Each call needs a modest amount of bandwidth — roughly 100 kbps per active line is a reasonable planning number — which is a small ask for most office internet connections today. The financial shift is bigger than the technical one: instead of a large upfront hardware purchase, most VoIP is priced as a monthly subscription per user, commonly in the neighborhood of $15 to $25 a month, with the desk phones or softphone licenses as the main hardware cost.
The tradeoff is dependency. A traditional PBX keeps working through an internet outage because it was never relying on the internet in the first place; VoIP goes down when your internet or power does, unless you’ve planned backup power and a failover connection into the install. That’s not a reason to avoid VoIP — most offices decide the cost and flexibility are worth it — but it is a real conversation to have before you sign a contract, not after the first outage.
The 911 Requirement You Can’t Design Around
Kari’s Law and the related RAY BAUM’S Act (which added a “dispatchable location” requirement — your exact address plus floor and room details) apply to multi-line systems generally, and they matter more with VoIP than they used to with a wired PBX. A traditional desk phone was physically wired to a jack in a specific room, so the phone company always knew where a 911 call was coming from. A VoIP extension can move with an employee’s laptop or ring on a mobile app from a different floor entirely, which means the dispatchable location has to be configured deliberately rather than assumed. This is exactly the kind of detail that gets missed when a business buys VoIP off a self-service website instead of having it installed and configured by someone accountable for getting it right.
What Actually Decides It for Most Offices We Wire
In practice, the decision usually isn’t “PBX vs. VoIP” in the abstract — it’s what’s already in the walls and what the business actually needs. An office with solid structured cabling and reliable internet is usually a good fit for VoIP, since the backbone is already there. A building without that infrastructure needs the network side addressed first, or a hybrid approach makes more sense while that gets built out. Businesses running fully remote or hybrid teams tend to lean VoIP for the mobile app and softphone flexibility; a business that wants a system that keeps working no matter what the internet is doing that day sometimes still chooses a traditional PBX, budget allowing.
One Disclosure Worth Making Plainly
MetroCom is an installer and systems integrator, not a manufacturer of phone system hardware or software. We design, install, and configure PBX and VoIP systems from established platforms as part of a project, and we handle the structured cabling and network side that either system depends on. We don’t build the phone systems themselves, and our recommendation is based on what your office’s infrastructure and call volume actually need, not on a single platform we’d rather install.
Frequently Asked Questions
Can an existing PBX be upgraded to support VoIP instead of ripping everything out?
Often, yes, through a hybrid setup or a gateway that bridges the two, especially if the existing wiring and network can support it. Whether that’s worth doing instead of a clean VoIP install depends on the age of the current PBX and what condition the cabling behind it is in.
Does a small office really need a full PBX, or is a key system enough?
For a handful of employees with simple calling needs, a key system can still be the right call on cost alone. Once you need call routing between departments, voicemail-to-email, or more than a couple dozen users, a PBX or VoIP system earns its cost back in the features it opens up.
Is VoIP call quality actually reliable, or does it sound choppy?
On a properly planned network with adequate bandwidth and correct configuration, VoIP call quality is generally indistinguishable from a traditional line. Quality problems usually trace back to insufficient bandwidth, network congestion, or a system that was never configured for the connection it’s running on, not VoIP as a technology.
What happens to 911 calls if the internet goes down on a VoIP system?
Without a backup plan, a 911 call on VoIP fails the same way any other call does during an outage. Offices serious about this pair VoIP with a cellular failover or a battery-backed connection specifically so 911 and other calls stay live during a network or power interruption.
What This Means for Your Office
If you’re weighing a phone system upgrade, the right starting point is an honest look at your existing wiring and network, not a features list from a vendor. MetroCom’s business telephone system installation covers PBX, VoIP, and hybrid setups end to end, and it’s frequently installed alongside our computer network and structured cabling services since a phone system is only as reliable as the network carrying it.
