My daughter is spending a year in the US, before returning to the UK; and her phone is malfunctioning, so she’s looking to buy a cheap second-hand replacement.
I know that back in medieval times, an iPhone sold in the US worked on different networks to the EU - e.g. at one point I think we had GSM in the EU, whereas US was on CDMA (?). But I don’t know if the technologies are still so distinct - or whether now every iPhone has all the circuitry for all the current networks?
Specifically, will an iPhone 7 sold in the US market work as well when she returns to the UK as one sold in the UK? Am I worrying unnecessarily?
It should work AOK if she switches in an appropriate SIM card. Be sure to check, and maybe even double check, in advance with her soon to be network carrier.
I also highly recommend buying a certified refurbished iPhone; she should get a year of Apple Care as part of the deal.
Back in those days, there were two competing standards in the US: GSM (and it successors) provided by AT&T and T-mobile. And CDMA (and its successors) provided by Verizon and Sprint.
Today, the tech has converged. Everybody is supporting LTE (4G) and 5G. The 3G and older tech (GSM and CDMA) are being turned off by network operators, so they are rapidly becoming a footnote.
As for an iPhone 7 (which is a pretty old model), see Apple’s specs:
There are two models: A1660 and A1778. There is only one difference, WRT cellular bands:
CDMA bands (TD-SCDMA and CMDA EV-DO) are only on the A1660
Both models support the same set of LTE (FDD-LTE and TD-LTE) and GSM (UMTS/HSPA+/DC-HSDPA/GSM/EDGE) bands.
So don’t worry about it. Buy whichever model you like. Just make sure it is unlocked so she can use a UK SIM card after returning home.
I’ve been on several trips in Europe - Faroe Islands, Amsterdam, Oslo, Iceland - in the last few years with Americans who had iPhones. None of them seemed to have the slightest difficulty in using them over here, whether for making calls or for data connection. FWIW.
My iPhone 7, bought in the US, worked fine in England and Ireland, as well as other parts of Europe. I simply replaced the US carrier chip for a local UK one.