The companies which provide cellphone / mobile phone services around the world.
Could someone please explain why? (phone-networks has no Usage guide).
I appreciate "operators" might cover the likes of O2, EE, Three Mobile, Vodafone, Mobile by Sainsbury's, Virgin Media, giffgaff, Tesco Mobile etc (that Google finds me from a search of phone networks) and that phone-networks might be more the likes of 1G, 2G, 3G, 3.5G, 3.75G, 4G, LTE etc. but it seems the tags are not used in this way at present on TSE.
Maybe also GSM-850, GSM-900, EGSM/EGSM-900, GSM-1800, GSM-1900 and UMTS are relevant.