GSM: What It Is, and Why It Just Ended in the US

GSM, Global System for Mobile Communications, is the digital standard that decides how a phone proves who it is to a network: how it registers, how a call gets encrypted, and how it gets billed to the right account. It matters today for one specific reason that survived the rest of the standard: GSM is what invented the SIM card, and an eSIM is a SIM by another name.

The letters started in French, as Groupe Spécial Mobile, the working group CEPT set up in the early 1980s to agree on one cellular standard for Europe rather than let every country keep building its own. GSM’s own radio technology is now old enough that carriers are retiring it outright: T-Mobile switched off the last major GSM network running in the United States on 3 August 2026. The SIM concept the same working group wrote did not go anywhere at all.

CEPT, the club of European telecom regulators, formed an ad hoc subgroup called Groupe Spécial Mobile in the early 1980s to build one digital cellular standard rather than let every country keep building its own, the way they had with analogue networks. According to 3GPP’s own account of the standard’s history, the group transferred into the newly created ETSI in 1988 and became ETSI’s own Technical Committee GSM in 1990. 3GPP itself was formed in 1998, and by mid-2000 it had taken over GSM’s radio specifications completely, closing the ETSI committee that used to hold them.

What began as a French working group’s name is now almost always expanded in English, as Global System for Mobile Communications. The initials survived that switch; hardly anything about the underlying radio technology did, since GSM’s 2G network is exactly the layer carriers are now busy switching off.

The SIM card was not bolted on afterwards. 3GPP’s own archive of the standardisation work lists the development of the SIM card as one of the specific things the GSM committees produced, tracked through a dedicated working group (SIMEG, later folded into SMG9) running alongside the radio specification itself. The idea was to separate the subscriber from the handset: identity, phone number and credentials live on a small removable module, so the phone underneath it is disposable and the account is not.

That split still does the job it always did. The GSM Association, the operator body built around this standard, marked the SIM’s own anniversary by saying it had “provided the security and authentication to access mobile networks for almost a quarter of a century”, a description from 2015 that has not needed updating since, even though the module itself has shrunk from a credit-card-sized card to a profile with no physical card at all.

Not every carrier built on GSM. Verizon and the old Sprint ran their networks on CDMA, a rival American standard with no technical relationship to GSM, and a CDMA phone proved who it was by the device itself rather than by anything a customer could remove and hand to another phone. That difference, not habit, is the real reason “unlock the phone and move the SIM” was always a GSM-world routine: there was no card to move on a CDMA one.

CDMA is gone as a live network in the US now. Verizon states plainly that it has decommissioned its CDMA network as of 3 January 2023, having moved what traffic was left onto SIM-based LTE like everyone else. GSM did not outlast CDMA by being the better radio technology so much as by being the standard the rest of the world had already settled on.

Winning that argument did not save GSM’s own 2G technology from being switched off. AT&T gave notice as early as 2015 that its 2G network would close on 31 December 2016, one of the first big US shutdowns; T-Mobile’s own coverage page lists 3 August 2026 as the date its 2G GSM network went dark, closing out the three big US carriers.

It is a global pattern, not a US one. GSMA Intelligence’s own 2025 industry report puts 2G and 3G combined at under 20% of the world’s mobile connections, and counts 152 individual networks already shut down by the end of November 2024, with another 131 scheduled by 2030. Somewhere on that second list is the last GSM network that will still be running the day you read this, though it is unlikely to be the one your own travel eSIM roams onto.

None of this means hunting for the word “GSM” on a spec sheet before a trip. Virtually every phone sold today, and every travel eSIM this site compares, runs on GSM’s technical descendants: 3GPP carried the same lineage forward through 3G, 4G and 5G, all of it still organised around the SIM the original GSM committees designed. Reading up on the actual difference between 4G and LTE covers the rest of that ladder, if you want it. The one real exception is a phone built solely for Verizon’s or Sprint’s old CDMA network from before the SIM-based LTE switch: it can still need an unlock or a firmware update before a foreign SIM works at all, even though the network it was bought for no longer exists to complain about it.

What decides the actual bill has never been the generation label anyway. It is which network a provider’s eSIM roams onto in the specific country you are visiting, and what that network charges for the data you will use there: plans by destination, compared on price per gigabyte rather than on which acronym is printed on the box.