Call overflow for taxi firms: what happens when the line is busy

Friday at 11pm, the controller is on one call and two more are ringing. Where those calls go is your call overflow, whether you planned it or not. This guide explains what callers hear on a busy taxi line, how the different diverts work, why the timing depends on your phone provider, and how to set up overflow and test it.

What is taxi call overflow?

Taxi call overflow is the plan for calls your office can't answer when they arrive. A call can't be answered for two reasons: the line is busy because someone is already on it, or the phone rings and nobody picks up. Overflow decides what happens next.

There are three answers. The call can fail, so the caller hears the engaged tone or ringing until they give up. The call can wait in a queue for the next free person. Or the call can overflow to somewhere that can take it, such as a second phone, a manager's mobile, an answering service or an AI phone agent.

What does a caller hear when your line is busy?

What a caller hears on a busy line depends on how your number is set up:

• One line, no extras. The second caller hears the engaged tone, and is free to ring someone else.
• One line with Call Waiting. On a BT business line, Call Waiting gives you a discreet beep when someone else is trying to get through, and you switch between callers. The second caller is still waiting on the one person who is already talking.
• A hunt group. Several phones share one number. On BT's Digital Voice for Business, a hunt group can ring phones in order, in a circle, all at once, or the one that's been free longest. In the ring-all-at-once mode, BT says that if everyone in the group is already on a call, the new caller hears a busy tone.

So adding phones helps until everyone is busy. After that, you're back to the engaged tone unless something catches the overflow.

What kinds of call divert are there?

A call divert sends calls from your number to another number when a condition is met. There are four common kinds, and on BT and Vodafone lines they use the same numbers:

You add the number to divert to after the code and finish with #. On a BT line, a code such as #61# cancels that divert, and \*#61# checks whether it's on.

The divert when busy and the divert for unanswered calls work well together for overflow: the office answers what it can, and the rest go on. The all-calls divert is the one for nights, when nobody is in the office at all. Our guide to covering nights without a night controller looks at the options for those hours.

How long before an unanswered call diverts?

How long a no-answer divert waits depends on your phone provider and the product, not on whoever takes the overflow. Here's what the providers' own help pages say:

So on a plain BT business line, BT's help pages give no way to shorten the 15-second wait. If 15 seconds feels long when the phones are going mad, the answer is the busy divert, which doesn't wait at all, or a product that lets you set the time.

Should you queue callers or overflow them?

A queue keeps the caller waiting for your own staff. An overflow sends the caller somewhere else that can answer now. For a taxi firm, the right choice depends on whether somebody will be free soon.

Some phone systems do both. BT's Digital Voice hunt groups can forward a call to a set number if nobody in the group answers in your chosen time, and send calls on to that number if all the group's phones are unreachable, for example in a power cut.

A queue at 2am with nobody in the office isn't a queue. It's a recorded message. For those hours you need overflow.

What does call overflow cost?

Call overflow costs you the divert feature, the diverted part of each call, and whatever answers the calls. BT's help pages say:

• Call Diversion is a paid-for feature on its phone lines, and it shows on your bill.
• The diverted part of each call is charged at BT's standard dialling rates.
• Smart Divert, which lets you divert remotely, has a minimum term of 3 months.
• Hunt groups on Digital Voice for Business come with the Enhanced and Extra packages, and each hunt group needs its own phone number, which is charged for.

Check your own provider's tariff before you switch anything on, and put the cost in your sums next to the bookings you'd otherwise lose.

What changes when your line goes digital?

The old analogue phone network is being switched off. The government says the telecoms industry announced the retirement of the PSTN in November 2017, and that all UK landlines need to be upgraded by January 2027. It also says over two thirds of UK landlines have already moved to internet calling.

For overflow, that means two things. Your divert codes and settings might change when your line moves, and digital products such as hunt groups give you more control over timing than a plain line ever did. Test your diverts again the day after your line is switched.

One more trap from BT's own troubleshooting page: if outgoing Call Barring is switched on, Call Diversion won't work. If a divert seems dead, check that first.

How do you set up and test call overflow?

Setting up overflow is a short job, and testing it is shorter:

1. Decide where overflow goes. A second phone, a manager's mobile, an answering service or an AI phone agent. Whoever answers must be able to take a booking, not just a message.
2. Check what your line can do. Look up your provider's divert page, or ask, and confirm the feature is on your account.
3. Set the busy divert and the no-answer divert. Use both, so calls go on whether the line is engaged or ringing out.
4. Set the all-calls divert for nights, or schedule it if your system allows.
5. Ring your own number from another phone. Let it ring out, then ring it while the line is busy, then ring it at night. Note what you hear each time.
6. Write the cancel codes down and keep them by the phone.

Our guide to missed calls in a taxi office shows how to count the calls you're losing before and after.

Dispatch AI's phone agent is one place overflow can go. You put it on the calls your office can't answer, when the line rings out and overnight, or on your whole booking line if you'd rather. You choose the hours, it works by a call divert on your own line, and each agent takes up to 10 calls at once. The AI phone agent guide walks through what happens on the call.