How call forwarding actually works, in plain English

Call forwarding has one job. A call arrives at your number, and the network sends it somewhere else instead of ringing your phone. What trips people up is the assumption that it's a single on or off switch. It isn't. There are four separate rules, they behave differently, and you can have several running at once without knowing it.

All four are defined in 3GPP TS 22.030, the standard behind the keypad codes, and the main ones exist on landlines too. What any given network actually switches on can vary, so check yours.

• Unconditional. Every call goes straight to the other number. Your phone never rings at all. EE describes this as diverting all calls without your phone ringing.
• On busy. The call forwards only when you're already on another call.
• On no answer. Your phone rings first, and the call forwards if you don't pick up in time. BT's landline service diverts calls you don't manage to answer within 15 seconds.
• On unreachable. The call forwards when the phone is off, out of signal or in flight mode. That's really a mobile idea. BT's landline diversion page lists three types and doesn't include an unreachable one.

The last three are called conditional forwarding, because each waits for a condition before it does anything. EE puts it plainly: conditional diverts divert calls based on certain conditions, for example your phone being busy or there being no answer. If you're setting up any kind of answering cover, the conditional rules are usually what you want, with unconditional left off. Your phone still rings first and you can pick up if you're free.

The codes aren't a network gimmick. They come from 3GPP TS 22.030, the standard that defines how a keypad talks to the network. Each service has a short code:

• 21 unconditional forwarding
• 67 forwarding on busy
• 61 forwarding on no reply
• 62 forwarding on not reachable
• 002 all forwarding rules at once
• 004 all conditional forwarding rules at once

The punctuation around the code decides what you're doing to it. The standard gives activation as *code*number#, deactivation as #code*number#, interrogation as *#code*number#, registration as *code*number# or **code*number#, and erasure as ##code*number#.

Before you set anything, ask the line what it's already doing. Dial *#21#, then *#61#, then *#67#, then *#62#. Each one reports back. BT lists the first three as its check codes on both the landline and Digital Voice pages, and Vodafone lists all four on mobile.

To set one on a Vodafone mobile, the published instruction is to dial **61* then the destination number then #, and cancel it with ##61#. Same shape for 21, 67 and 62. If you've lost track of what's on the line, ##002# clears every divert in one go, which is the safest way to get back to a known state.

One useful extra: the standard gives forwarding on no reply a No Reply Condition Timer, entered after the destination number, so you can ask for a longer or shorter ring before it gives up on you. Not every network exposes it, so treat it as worth a try rather than a guarantee.

This is the part that catches people out. The forwarded leg is your call, and you pay for it. The caller pays to ring your number. You pay to push it onwards. BT's landline page says you'll be charged for the duration of any diverted calls, plus the standard call setup fee.

Beyond that it varies by network and by where you're sending the call:

• BT says Call Diversion is inclusive for Digital Voice customers, and that the cost of a diversion depends on the duration of the diverted call and the type of number you're diverting to.
• EE says setting up or changing a call divert to voicemail is free for EE Small Business customers, and that diverts to other UK numbers come out of your allowance, with standard charges once you're past it.
• Vodafone says that on Pay monthly, or a Pay as you go Big Value Bundle, diverting calls to voicemail will use minutes from your allowance.

The practical read is that forwarding to an ordinary UK landline or mobile costs you roughly what ringing that number yourself would cost. If you're forwarding to an 08 number, check the rate first. None of the network pages I've checked publish a per-minute forwarding rate, so check your own tariff rather than taking a figure off a blog.

On a mobile the codes go through the handset and take effect in seconds. Worth knowing: the rule lives on the network, not in the phone. So if you're not sure what's set, dial the check code rather than assuming a new phone cleared it.

Landlines are less uniform. BT's troubleshooting page says a divert can fail because the service isn't active on the line, because the setup sequence was entered wrongly, because Outgoing Call Barring is switched on, or because the phone isn't set to tone dialling. If a code won't take, that's the list to work through before you ring anyone.

There's a bigger change underneath all of it. The old analogue phone network is being retired, and BT Business gives the date as 31 January 2027. Your landline becomes a digital line carrying calls over broadband. Diversion doesn't disappear. BT's Digital Voice page lists the same *21*, *61* and *67* codes. But on some digital handsets you set it through a voice menu under Calling Features instead of dialling, and where you manage it online has moved around.

Here's the bit that matters if you're weighing up an answering service of any kind. Forwarding doesn't change your number. It changes where calls to your number end up. Nothing moves, transfers or ports. Your number still rings at your number first.

So the number painted on the van, cut into the shopfront, sitting under years of Google reviews and printed on every quote you've ever sent stays exactly as it is. Customers dial the same digits they always did. All that changes is the fallback. Instead of an unanswered call ringing out to voicemail, it lands somewhere that picks up.

It's also reversible in one dial. #61# on a BT landline, ##61# on a Vodafone mobile, and the divert is off. That's the entire undo. Anything that asks you to publish a new number, or to hand over control of your existing one, is asking for something forwarding simply doesn't require.

Forwarding is plumbing. It decides where a call goes. It has no opinion on whether the thing at the other end is any use, and that's where the actual value sits.

Voicemail is the default destination and it's the weak link. Plenty of people ringing a trade won't leave a message. They ring the next name on the list. Forwarding to your own mobile only helps if you can answer your mobile, which is no good on a roof or under a sink. Forwarding to a family member works right up until they're busy too.

That's the gap I fill. An AI receptionist sits on the far end of your conditional diverts, answers, takes the caller's name, number and what they need, and texts it straight to you. Your number doesn't change. You choose which diverts to switch on, so you decide whether it covers after hours, weekends, overflow or the lot. Pricing is a flat monthly fee with no per-minute billing, on 30 day rolling terms. There's more on how it works for trades and across Northern Ireland.

The honest caveat: if you already answer nearly every call, forwarding to anything is solving a problem you haven't got. Work out roughly what you're missing before you spend money on it. The missed call calculator takes a minute. If the answer is one or two calls a month, leave it well alone. If you're not sure, get in touch and I'll tell you straight, or read the rest of the blog first.