Useful Smartphone Codes Every Business User Should Know

Last winter a client rang us in a flap. One of his engineers had left a company handset in the back of a taxi somewhere between Telford and Birmingham, and the office had no record of the IMEI number. Without it, the network could not blacklist the device, the insurer wanted paperwork nobody had, and the asset register simply said "Samsung, black". That single missing 15 digit number turned a five minute job into a fortnight of chasing. The frustrating part is that the IMEI was sitting inside the phone the whole time, retrievable in about three seconds with a code most people have never heard of.

We have been arranging business mobile fleets from our base in Shrewsbury for eighteen years, and over that time we have come to see these dialler codes the way a tradesman sees a decent multimeter. Nobody talks about them, they are not glamorous, but when you need one you really need one. So this is the practical guide we wish more business mobile users had: the codes that genuinely earn their keep when you are running phones for a team, the ones to treat with respect, and the few you should never touch.

A quick word on what these actually are. Most of the codes below are USSD strings, short sequences starting with a star or hash that you type into the ordinary phone dialler and then call. The phone reads them as instructions rather than a number to ring. Some work on virtually every handset on the planet because they are baked into the GSM standard. Others are specific to one network or one manufacturer, and that distinction matters enormously, which is why we have flagged it throughout.

The one code everyone should know: showing your IMEI

If you remember nothing else from this article, remember star hash zero six hash. Typed as *#06# into the dialler, it instantly displays the handset's IMEI, the unique 15 digit serial number that identifies that specific device on any network anywhere. It works on essentially every mobile phone made in the last two decades, iPhone or Android, flagship or budget. There is no risk in running it. It simply shows a number on screen.

For a business this is the single most useful thing on the list, and here is why. Your IMEI is what a network uses to blacklist a stolen handset so it cannot be used again. It is what your insurer will ask for. It is what lets you tie a physical device to a particular line, a particular employee and a particular contract in your asset register. We tell every client building a fleet to capture the IMEI of each handset on the day it is issued, photograph the on screen number, and store it against the staff member's name. Do that once and the taxi scenario above becomes a phone call that takes minutes, not weeks.

If you manage more than a handful of devices, this habit alone justifies a proper asset spreadsheet. When we help businesses reduce their mobile costs, one of the first things we find is companies paying for lines tied to handsets nobody can locate. An IMEI log fixes that at source.

The codes worth keeping in your back pocket

Below is the table we hand to office managers. Treat the GSM standard codes as broadly reliable, and double check anything marked network specific with your provider before relying on it, because they genuinely do differ between EE, Vodafone, O2 and Three.

Notice we have deliberately kept this list tight. There are dozens of so called secret codes floating around online, and a fair number of them are either made up, region specific to phones never sold here, or genuinely dangerous. We would rather give you eight codes we trust than forty we cannot vouch for.

Checking call forwarding, the silent productivity killer

Of all the support calls we field about handsets that "are not working", a surprising share come down to call forwarding that nobody set on purpose. A member of staff thumbs through a settings menu, a divert gets switched on, and from then on their phone never rings while callers reach a voicemail they never check. For a sales line or a customer facing mobile, that is lost revenue happening quietly in the background.

The interrogation codes in the table let you diagnose this in seconds without digging through menus. Dial *#21# to see if everything is being unconditionally diverted. Dial *#62# to see where calls go when the phone is switched off or out of coverage, and *#67# for when the line is engaged. The phone responds with the destination number or tells you the divert is not set. If you find a rogue divert and want a clean slate, ##002# wipes the lot, though do pause before you use it, because legitimate setups like out of hours routing to a central number will also be cleared.

This is exactly the kind of thing worth checking across a fleet periodically. We have walked into businesses where a third of the team had stale diverts left over from a previous handset, and switching them off restored calls people did not even realise they were missing.

Voicemail and network shortcodes

Voicemail access is the area where we most often have to say "it depends", because it is heavily network specific. Many UK networks use a shortcode you dial directly rather than a star and hash USSD string, and that shortcode is not the same across providers. Rather than print a number that might be wrong for your network and send you to the wrong place, our honest advice is to confirm your voicemail and customer service shortcodes with your provider or check the welcome material that came with the SIM.

The same caution applies to customer service numbers. You will see 150, 191 and similar shortcodes quoted online as if they are universal. They are not. They have shifted over the years and they differ between networks, so treat any single number you read as a starting point to verify, not gospel. If you are unsure which network a line even sits on, that is itself a sign your fleet records could be tidier.

Reading your actual signal strength

Here is a trick worth knowing if you ever argue with a network about coverage. The signal bars on your screen are close to meaningless. They are a marketing friendly approximation with no agreed standard, so four bars on one handset can be weaker than two bars on another. The real measure is signal strength in dBm, a negative number where closer to zero is stronger. Roughly speaking, around minus 70 dBm is excellent, minus 90 is workable, and minus 110 or below is where calls start dropping.

Most phones can show you this true figure, though how you reach it varies by manufacturer rather than by a single universal code, which is why we have not printed one specific string in the table. On many Android handsets it lives under Settings, then About phone, then Status or SIM status, where you will find signal strength listed in dBm. On iPhones the old field test code that used to surface this has been changed and restricted across recent iOS versions, so we would not promise any particular dialler string still works there. The reliable route on either platform is the settings menu.

Why does this matter for a business? Because when staff complain a site has poor coverage, a dBm reading turns a vague grumble into evidence. We have used these numbers to push networks for a signal booster, to justify moving certain lines to a different provider, and to settle the perennial debate about whether the problem is the building or the network. When you genuinely compare business mobile plans on coverage rather than headline price, real signal data from the actual sites your team works in is worth far more than a coverage map.

The codes to leave well alone

Now the warning, because it matters. Not every code is harmless. The internet is full of lists that bury genuinely destructive strings among the useful ones, and on some handsets, particularly certain older or specific Android models, there are dialler codes that trigger a full factory reset, wiping the device the moment you press call, with no confirmation prompt. On a personal phone that is a bad afternoon. On a business handset full of contacts, authenticator apps and saved logins, it is a serious incident.

Our rule is simple and we give it to every client. Never enter a code you found online without understanding exactly what it does, and never run anything described as an engineering, service, reset or wipe code unless a manufacturer or your network has told you to as part of a specific support process. The interrogation codes in our table are read only by design, they show information and change nothing, which is why we are comfortable recommending them. Anything that promises to unlock hidden menus, run diagnostics or modify settings should be treated as off limits on a working business device. If a handset genuinely needs a reset, do it through the proper Settings menu where the phone asks you to confirm, not through a dialler shortcut that does it instantly.

One more practical safeguard for fleets. Make sure every business handset is enrolled in Find My iPhone or Find My Device and, ideally, a basic mobile device management setup, so that a lost phone can be located, locked and wiped remotely on your terms. That gives you the genuine reset capability you might occasionally need, with proper control, rather than relying on risky codes.

Tying this back to managing your fleet

Step back from the individual codes and a theme emerges. Every one of these tricks is really about visibility and control over the devices your business depends on. Knowing each handset's IMEI, knowing where calls are diverting, knowing the true signal at each site, knowing which device belongs to which line. These are the unglamorous fundamentals that separate a fleet that runs itself from one that generates a steady drip of problems.

The same logic applies to the contracts underneath those handsets. Plenty of businesses we speak to have never audited their mobile estate at all, and when they finally do they find duplicate lines, handsets sitting on tariffs that stopped making sense years ago, and devices nobody can account for. Getting the basics straight, the asset register, the IMEI log, the divert check, naturally leads to the bigger question of whether you are on the right deal in the first place.

That is where we come in. As Compare The Networks, the trading name of Xtra Phones UK Ltd, we have spent since 2008 helping more than 2,000 UK businesses get their mobile fleets onto sensible contracts. We are OFCOM regulated and ICO registered, we hold a 4.3 out of 5 rating across more than 1,000 Trustpilot reviews, and we compare deals across EE, Vodafone, O2 and Three so you do not have to. Business mobile plans start from £11 plus VAT per month, and we will tell you honestly when your current deal is already a good one. If you want a clear look at the wider market, our guides on the best business mobile deals in the UK and on whether to standardise your fleet are a good place to start, and you can always compare business mobile deals directly.

If your asset register is a mess, your contracts are a patchwork, or you simply want to know whether you are overpaying, get in touch. We will get you a free, no obligation quote across all four major networks and help you sort the fleet, codes, contracts and all.