An eSIM (embedded SIM) is a small chip permanently soldered into a phone, smartwatch or tablet. Unlike a traditional SIM card you slide in and out of a tray, an eSIM stays in the device — you provision it by scanning a QR code or selecting a plan from a carrier's app.
How it works
The eSIM chip can hold multiple carrier profiles at once. When you activate Fuse, the carrier's provisioning server (called an SM-DP+) sends a digital profile to your phone over the internet, and your phone stores it on the eSIM hardware.
Why it matters
- Activate in minutes — no shop visit, no plastic in the post
- Switch providers without changing physical SIMs
- Run multiple lines on one device (e.g. work + personal)
- One less component to break or lose
See also
How eSIM matters when picking a UK mobile plan
Understanding eSIM helps you compare mobile providers on a like-for-like basis. Most consumer mobile pricing pages skip the technical detail — knowing the terminology means you can spot when a plan is genuinely better and when it just sounds that way. The Fuse Mobile glossary keeps definitions short and consumer-focused, no jargon-on-jargon.
Fuse Mobile is a UK multi-network data-only eSIM — it gives your phone access to all four UK mobile networks (EE, Three, Vodafone, O2) through a single profile. Where eSIM is relevant to that setup, it's surfaced explicitly: pricing pages show real numbers, the coverage checker shows live per-network signal, and there's no hidden fee structure. See the plans page for the current pricing or read the multi-network eSIM explainer for the technical detail.