Which network does your SIM actually use?

Only four companies own mobile masts in the UK: EE, O2, Three and Vodafone. Everyone else rents. That single fact explains most of the SIM market, because two SIMs on the same masts get the same signal at your address for very different prices. This guide maps every network we compare to the masts it actually uses, answers the coverage question honestly, and shows you the two-step trick that gets big-network signal on a small-network bill.

The host map

The eighteen networks we compare on Switchity all rent from the same four mast owners, and the table below shows who is on whose masts, straight from the catalogue behind our comparison. Click any network to see its live deals.

The pattern worth noticing: every mast owner has a family of cheaper networks living on its signal. Three carries iD Mobile and Smarty. O2 carries giffgaff, Tesco Mobile and Sky Mobile. Vodafone carries Voxi, Talkmobile, Lebara and Asda Mobile. EE carries spusu, Lycamobile, Ecotalk and Grade Mobile. Whichever network wins at your address, there is almost always a cheaper way to buy its signal.

Do smaller networks get the same coverage?

For coverage, yes. A virtual network, or MVNO, buys wholesale access to its host's masts, so the coverage footprint at your postcode is the host's footprint. If Three reaches your kitchen, iD Mobile reaches your kitchen. Our guide to which network has the best coverage has the Ofcom numbers per host, and they apply to every brand on those masts.

Some honest caveats, though. The coverage is identical, but a few other things are not. At the busiest times a host can manage its own customers' traffic differently from its wholesale traffic, so an MVNO may occasionally feel slower in a packed stadium or station. Newer features can lag; 5G, Wi-Fi calling and eSIM sometimes arrive on the host months or years before its tenants get them. And since the 3G switch-off, calls in 4G-only areas depend on the network having enabled 4G calling; most have, but it is worth confirming on a smaller network if you live somewhere remote. Customer service, meanwhile, belongs to the brand you pay, not the mast owner. None of that changes the signal itself; it changes what your plan can do with it.

Who actually owns whom

Knowing the landlord is half the picture; knowing the owner is the other half, because several "rivals" are the same company wearing two badges.

Some tenants are in-house budget brands. Smarty is Three's own; Voxi and Talkmobile are both Vodafone's; giffgaff is owned by O2's parent. These exist so the big network can fight at the cheap end of the market without discounting its main brand. That is good news for you: the host has every incentive to keep its own budget brand's service solid. Tesco Mobile sits in between, a long-running joint venture between Tesco and O2.

Others are genuinely independent companies renting capacity, such as Lebara, Lycamobile and spusu. iD Mobile sits in this camp too, owned by the retailer Currys rather than any network. Independence cuts both ways. They can be sharper on price because nobody is protecting a premium brand upstairs, but their fortunes are their own, which is why the closing-down question below is worth two minutes.

The greener newcomers

A newer group competes on conscience rather than just price. Ecotalk runs on EE and puts profits into buying land for nature. Rewild Mobile funds rewilding projects and spreads itself across Three and Vodafone masts. Grade Mobile and Mozillion pair EE airtime with refurbished phones, attacking the waste side of the industry rather than the tariff side.

The same host-network logic applies: the green positioning changes where the money goes, not where the signal comes from. If the ethics matter to you, you can pick them with no coverage sacrifice against their host, and every one of them appears in our comparison with its host marked.

Why the same masts cost different money

Cheaper is not a trick; it is a different cost base. The big four pay for masts, spectrum, shops on the high street and prime-time advertising. A virtual network pays a wholesale rate for capacity and runs online: no mast upkeep, no store leases, support through an app or a forum rather than a call centre you can walk into.

You give up some extras in exchange. The hosts bundle roaming perks, device plans and loyalty schemes that tenants rarely match. If none of those matter to you, and for most SIM only buyers they do not, the wholesale price is the same signal with less packaging.

How to use this when you choose

Two steps, in this order, and the first one costs nothing.

First, find the network whose signal wins where you live. Check your address on Ofcom's mobile coverage checker, which shows all four mast owners side by side, and use our UK mobile coverage map for how your wider area compares. Judge the host, not the brand; the brand is just the bill.

Second, shop across everyone on the winning masts. If EE wins at your address, compare spusu, Lycamobile, Ecotalk and Grade Mobile alongside it. If O2 wins, giffgaff, Tesco Mobile and Sky Mobile are the price competition. Every deal on our SIM only comparison shows its host network, so you can filter your shortlist to the masts that won.

Do the big four share masts with each other?

Partly, and it is worth untangling because it confuses people. The four operators share some physical mast sites in pairs to cut costs: EE with Three, and O2 with Vodafone. But sharing a site is not sharing a network. Each operator hangs its own equipment and runs its own spectrum on those shared structures, which is why EE and Three can stand on the same hilltop and still cover your valley differently.

So the sharing does not collapse the map above. The wholesale renting in the table is a different arrangement entirely: an MVNO transmits on its host's actual network, spectrum and all, which is why its coverage is identical to the host rather than merely similar. Judge the four hosts as four separate footprints, then treat every tenant as a perfect copy of its landlord.

A worked example pulls it together. Say Ofcom's checker shows EE strongest at your address, Three patchy indoors. That rules out iD Mobile and Smarty along with Three itself, and rules in spusu, Lycamobile, Ecotalk and Grade Mobile along with EE. Your shortlist went from eighteen networks to five in one postcode check, and the cheapest of the five gets you the best signal in the house at the lowest price anyone sells it for.

Switching hosts and switching brands

This map also tells you how risky a switch is. Moving between brands on the same masts is zero-risk on coverage; a giffgaff SIM cannot get worse O2 signal than O2 itself. Moving across hosts is where you re-run the address check first, because you are changing the masts, not just the bill.

Either way, the move itself is one free text. Our guide to switching and keeping your number covers the PAC process; the switch completes within one working day and your number comes with you.

What if a virtual network closes down?

It happens occasionally; smaller brands merge, rebrand or bow out. The protections are better than people fear, and they exist whatever the size of the brand you picked. Your number is yours to take: text PAC to 65075 and port it to any other network, exactly as our switching guide describes. A closing network has to give notice, and because most MVNO plans are 30-day rolling or short contracts, you are rarely locked into anything long anyway.

The practical hedge costs nothing: prefer short contracts on the smallest brands. A 30-day plan on an independent MVNO gives you its price with a four-week exit, which turns the worst case from a headache into an errand. The signal itself never disappears; the masts belong to the big four, and they are going nowhere.