Try this script:
local link = "http://ip-api.com/json"
local HttpService = game:GetService("HttpService")
local result = HttpService:Getasync(link)
print("User's carrier is:".. result.ISP)
This returns the ISP so if they are on 4g/5g it will show their carrier (e.g EE, Three, Vodafone, O2, Sky Mobile, etc.) Or on WiFi their ISP (e.g BT, Sky, Plusnet, Vodafone, etc.)
I visited this link on 5G and here’s the result:
{"status":"success","country":"United Kingdom","countryCode":"GB","region":"ENG","regionName":"England","city":"Oxford","zip":"OX2","lat":51.4566,"lon":-0.968,"timezone":"Europe/London","isp":"Hutchison 3G UK Ltd","org":"H3G UK","as":"AS206067 Hutchison 3G UK Limited","query":"92.40.213.141"}
(Hutchinson 3G is the corporate name for Three)
Hope this helped! 