eSIM and roaming glossary: the words networks and eSIM shops use

eSIM

An eSIM is a SIM built into the phone: you download a plan instead of fitting a card. Apple says an iPhone XS, iPhone XR or later takes one (bar some models sold in China mainland, Hong Kong and Macao) and can “manage up to eight or more eSIMs”. What is an eSIM.

eSIM profile

The downloaded plan that sits on the eSIM chip, one per line; a phone can hold several. Turning a line off can be undone, deleting it cannot: Apple says you then “need to contact your network provider to get a new one”. Move or remove an eSIM.

eUICC

The technical name for the chip that stores eSIM profiles. You never handle it; what matters is whether your phone has one. Check whether your phone takes an eSIM.

EID

The EID is the number that identifies your phone’s eSIM chip. Dial *#06#: if a line called EID appears, the phone has an eSIM. EE calls this “the quickest way to check that your device supports eSIM”. eSIM compatible phones.

QR code / activation code

The QR code is what you scan to download an eSIM; the activation code is what you type instead when the camera won’t read it. O2’s advice: “Never share your QR code with anyone and keep it somewhere safe.” How to install a travel eSIM.

SM-DP+ address

The address of the server the phone downloads the eSIM from. You type it with the activation code when you enter the details by hand, and our order e-mail carries both beside the QR code. Enter eSIM details by hand.

Activation on first connection

Most of our plans start their validity when the phone first connects to a network at the destination, not when you buy or install; each plan shows its activation rule. Almost all of them give you 365 days to install. How a travel eSIM works.

Data-only plan

A plan with mobile data and no minutes, texts or phone number. Our regional plans are data only; a few local plans add local calls, and none lets you call home or comes with a UK number. Calls and texts on your UK number.

Unlocked phone

A phone not locked to one network, so it takes another provider’s eSIM. On an iPhone, Settings → General → About shows “No SIM Restrictions” next to Network provider Lock when it is unlocked. Unlocked phones and eSIM.

Dual SIM

Two active lines in one phone. Apple: “Dual SIM enables you to have two active phone numbers”, and an iPhone “can use one mobile data network at a time”. So the UK line keeps calls and texts, which your UK network charges for abroad, while a travel eSIM carries the data. Keep your UK number.

APN

Access Point Name: the setting that tells the phone how to reach a network’s mobile data. Google says it helps “your operator find the right IP address for your phone”. On iOS 16 or later an iPhone fills it in automatically. eSIM not working abroad.

Data roaming

A setting on each line that lets the phone use other operators’ networks outside its own network’s coverage. A travel eSIM line needs it on. On your UK line, off stops foreign data, but a call you make or a text you send can still start a daily charge. What is data roaming.

Current period roaming

An iPhone usage counter, not a switch. Apple’s UK page lists data used “from a current period” and by apps “that used data when you were roaming”. The count runs from the last Reset Statistics, so it need not match your bill. Current period roaming on an iPhone.

Roaming charge (daily charge)

A flat charge for each day you use your UK plan abroad, on plans that don’t include the destination. EE counts the day “midnight to midnight, UK time”. On Vodafone one call made or text sent makes a charged day, and data roaming off does not stop it. UK roaming charges by network.

Roaming pass / day pass

A pass unlocks your UK allowance abroad for a set time, in place of a daily charge or per-MB rates. EE’s Weekly EU Roaming Pass runs for 168 hours from purchase. Sky’s Roaming Passport Plus lasts 24 hours and starts only with a call you make, a text you send or more than 10MB of data. Receiving calls and texts does not start it. Sky Mobile roaming.

Roam Like Home

A network’s name for using your UK allowance abroad as you would at home, within that network’s limits. BT’s Roam Like Home covers 47 destinations; Lebara’s covers the EU, the EEA and India, up to 30GB. Lebara roaming.

Travel Inclusive Zone

O2’s included roaming zone outside Europe: 27 countries of its Zone 1, the USA among them. It comes with Volt and selected Plus plans, not 30-day SIM only, and data there is capped at 2Mbps. O2 roaming.

Fair use policy

The limit a network puts on included roaming. Three lets pay monthly customers use up to 12GB of their allowance in any Go Roam destination. Vodafone’s pay monthly limit is 25GB, with £3.84 a GB above it. On travel eSIM plans, fair use means a daily amount at full speed, then a lower speed. Fair use on travel eSIM plans.

Roaming zone

A group of destinations a network prices the same way. EE has a Europe zone and Rest of World Zones 1 to 4, plus Zone 4* with no passes. Vodafone starts at Zone A, which includes Ireland and the Isle of Man. EE’s roaming zones.

Crown Dependencies

Jersey, Guernsey and the Isle of Man, which each UK network treats its own way. O2 and BT include all three, while EE charges its daily rate in all three and in Gibraltar. None of the three is in our Europe plan; Gibraltar is. Crown Dependencies and Gibraltar.

Maritime roaming

Your phone joining a satellite or ship’s network at sea or on a ferry. It costs far above normal roaming: EE £16 per 10MB, Three £6 a MB. A travel eSIM works on land networks in port, not at sea. Phones on a cruise.

Accidental roaming

Your phone joining a foreign network without you crossing a border, for example near Northern Ireland, on a coast or at sea. Ofcom’s C3.17 requires networks to explain it and how to limit it. In Greece or Cyprus, EE’s fix for a Turkish network is to text EUROAM to 150. Roaming in Europe.

Ireland (Republic of)

Treated like home on all 15 UK networks we checked, so you don’t need a travel eSIM there. Several networks say so to protect you from accidental roaming at the Northern Ireland border. Is Ireland included.

Spend cap / bill limit

A limit on roaming charges, set by your network or by you, that you can change or remove. Ofcom requires networks to warn you before the limit and not to charge above it without your consent. The legal £45 cap ended in June 2022. What Ofcom requires.

PAYG / pay monthly / SIM-only

PAYG means you pay from credit you top up. Pay monthly is billed each month, often with a phone, and SIM-only is a monthly plan without one. Roaming terms differ between them: Three’s Around the World Extra band is not available on PAYG. Roaming on every UK network.

SIM hibernation (PAYG)

What happens to a pay-as-you-go SIM you stop using: after a period without use, a network can suspend or close it. The period, and whether you keep the number, are each network’s own rules, so check yours before a long stay abroad.

Bolt-on / add-on

Extra roaming allowance bought on top of your plan. O2 sells Data Roaming Bolt Ons, Vodafone sells Extras and Lebara sells add-ons; some work on pay monthly only. O2’s bolt-ons.

Top-up

Credit or data added to a line after you buy it. Our plans can’t be topped up at the moment, so buy enough data for the whole trip.

Hotspot / tethering

Sharing your phone’s mobile data with another device over Wi-Fi. Apple says Personal Hotspot “requires a wireless network provider that supports Personal Hotspot”; our plan pages state no hotspot rule, so message us before relying on it. See our hotspot guide.

4G / 5G

Generations of mobile network. Each of our plans lists its network type per country, and we write 5G only where that plan’s data says so.

Ofcom General Condition C3

Ofcom’s rules, in force from 1 October 2024, on what UK networks must tell their roaming customers. They cover the arrival message (C3.15) and a message when the included allowance is used up (C3.13 and C3.14). C3.16 adds a free opt-out and opt-in, and C3.17 clear information on accidental roaming. Ofcom’s roaming rules.

Arrival message (Ofcom C3.15)

The free text your network sends when your phone connects abroad, unless you opted out. Under C3.15 it says whether the destination is in your plan and gives prices per minute, text and GB. It also gives any recurring charge, with when it starts and ends, and the fair-use limits. The arrival text and Ofcom’s rules.

BTK

Turkey’s telecoms regulator. Since 10 July 2025, according to press reports, it has blocked access from Turkey to foreign eSIM sellers’ websites and apps (reported by Teknoblog, 11 July 2025, in Turkish). Buy and install your eSIM before you travel. eSIM in Turkey guide.

Sources checked: Ofcom: mobile roaming customer protections · Ofcom: guidance on General Condition C3, 1 October 2024 (PDF) · Apple: eSIM on iPhone · Apple: Dual SIM · Apple: erase an eSIM · Apple: mobile data usage · Apple: Personal Hotspot · Apple: APN settings · Google: Pixel mobile network settings · EE: download and use an EE eSIM · EE: price guide, 31 March 2026 (PDF) · EE: get ready to roam · O2: eSIM help · O2: Travel Inclusive Zone · Three: Go Roam · Vodafone: global roaming · Sky: Roaming Passport Plus · BT: what is Roam Like Home · Lebara: roaming rate finder.