The GlobeSurfer III used a standard 2FF (Mini SIM) plastic card. Fifteen years later, the SIM itself has been redesigned, standardised for remote provisioning, and embedded directly into device hardware. This guide covers the full arc from physical SIM to eSIM - and explains the roaming and multi-network SIM options available for modern routers.
The SIM card (Subscriber Identity Module) has been progressively miniaturised since the 1G era. The GlobeSurfer III used a 2FF (Mini SIM) - the large-format card that dominated from the 1990s into the 2010s. Form factor reductions followed consumer device trends: 3FF (Micro SIM) arrived around 2010, 4FF (Nano SIM) in 2012.
Physical size reduction was driven by mobile phones needing more internal space for batteries and other components. Router manufacturers adapted accordingly - most modern 4G and 5G routers use Nano SIM or dual SIM slots with a multi-format tray accommodating both Micro and Nano.
eSIM removes the physical card entirely. The SIM functionality is embedded as a chip on the device PCB (eMBB/eUICC - embedded Universal Integrated Circuit Card), and mobile operator profiles are downloaded over-the-air (OTA) rather than inserted physically.
For consumer devices (phones, tablets, wearables), eSIM means switching operators without swapping a physical card. For routers and IoT devices, the implications are more significant - a device deployed in a remote location can have its SIM profile changed, updated or switched to a different operator without physical access.
Three GSMA specifications define eSIM behaviour. SGP.02 covers M2M eSIM for industrial devices, using a machine-to-machine profile management architecture. SGP.22 covers consumer eSIM - the standard used in iPhones, Android phones, and an increasing number of consumer routers. SGP.32 is the newest standard, specifically designed for IoT devices at scale - lower cost, lower power, simpler architecture than SGP.02.
For detailed technical coverage of SGP.32 and the eUICC ecosystem, see sgp32.co.uk and euicc.co.uk.
| 1FF (Full SIM) | 85.6 x 54mm - credit card size |
| 2FF (Mini SIM) | 25 x 15mm - GlobeSurfer era |
| 3FF (Micro SIM) | 15 x 12mm - 2010 onwards |
| 4FF (Nano SIM) | 12.3 x 8.8mm - current standard |
| MFF2 (eSIM) | 5 x 6mm soldered chip - IoT |
| iSIM | Integrated in SoC - no separate chip |
| SGP.02 | M2M eSIM - industrial/legacy IoT |
| SGP.22 | Consumer eSIM - phones, tablets |
| SGP.32 | IoT eSIM - mass-scale devices |
A roaming SIM is a SIM card that maintains data connectivity across multiple countries using roaming agreements rather than being locked to a single domestic network. For router use, roaming SIMs matter in two scenarios: devices that physically move between countries (vehicles, equipment, personnel), and devices in fixed locations where roaming SIMs offer better commercial or technical terms than domestic alternatives.
A multi-network SIM goes further - it connects to whichever of several networks provides the best signal at a given location, switching dynamically. For routers in challenging or mobile environments, a multi-network SIM effectively aggregates coverage from multiple operators on a single SIM. This is particularly valuable in rural UK where coverage gaps on individual networks are common.
| SIM Type | Best Use Case | Operator Lock | Typical Cost |
|---|---|---|---|
| Standard consumer SIM | Fixed home/office, good single-network coverage | Single operator | Low - £5-15/month |
| Roaming data SIM | International travel, multi-country vehicles | Home + roaming partners | Medium - per-country rates |
| Multi-network SIM | Rural deployments, vehicles, unreliable coverage | None - steers to best signal | Medium - typically IoT pricing |
| IoT / M2M SIM | Industrial, commercial, fixed IP required | Varies by MVNO | Variable - pooled data common |
| eSIM (SGP.22) | Consumer devices, switchable operator | None - OTA profile switch | Same as standard |
| eSIM (SGP.32) | IoT at scale, remote provisioning | None | Low - designed for volume |
For roaming SIM cards compatible with 4G and 5G routers, see roamingsims.co.uk. For multi-network options, see multinetworksim.com. For IoT and M2M-grade SIMs with management capabilities, see iotsims.co.uk.