What is a PBX?

Before it existed, every phone needed its own line to the exchange. A business with thirty desks paid for thirty lines, most of them idle most of the day.

The exchange fixed that by sitting between the desks and the network. Internal calls never leave the building, and external ones share a smaller pool of lines.

Everything you think of as business phone behavior lives here. Extensions, hold, transfer, hunt groups, the menu that answers after hours.

The box itself has mostly gone. The rules survived and moved to software, which is the whole story of the last twenty years in this corner of telecoms.

Say a law office has twelve people and four outside lines. At 10:15 on a Monday, three attorneys are on client calls and the receptionist is talking to the court clerk. All four lines are in use, and the fifth caller gets a busy signal.

A paralegal then dials extension 108 to ask a partner a question. That call never touches an outside line, because the exchange connects the two desks internally. The office could have fifty internal calls going and still have only four paths to the outside world.

This is the arithmetic that decides how a system gets sized. Twelve people don't need twelve lines, because they're rarely all on external calls at once. But on the day a big case hits the local news and everyone's phone lights up, four lines is a hard ceiling. Callers who hit it hear a tone that sounds like the firm has closed.

Before you change anything about a phone system, write down what the current one does. Most offices discover rules nobody remembers setting up, and those are the ones that break quietly in a move.

Walk through it with a notepad. What happens when someone dials the main number at 7:00 at night? Which phones ring when the receptionist is at lunch? Is there a fax line, a door buzzer, an alarm panel or a credit card terminal that dials out through the same box? Does the elevator phone run through it?

Check the hunt group order too. Often the list still includes someone who left two years ago, and calls ring an empty desk for 15 seconds before moving on.

Your inventory usually fits on a page and takes an hour. It's also the document a vendor needs for an accurate quote. Keep it as your test checklist for the first morning after any change, even one as small as adding an answering path in front.

GreetKeeper sits in front of whatever you have. Your existing system keeps doing its job, and calls it cannot cover get forwarded to the assistant.

That means no rip and replace. You are adding an answering path, not migrating a phone system, and you can undo it by canceling the forward.

Transfers hand the call back to your extensions the ordinary way, so the rules you already built keep working.