Three

United Kingdom ★★★ Verified Customer: 333

Three UK is the UK's fourth-largest operator, founded 2003 (UK's first 3G network), owned by CK Hutchison. In June 2025 merged with Vodafone UK to form VodafoneThree. Around 13% market share. **Note: Three relies primarily on the My3 app and has very limited USSD support** — no standard USSD balance query. Customer care 333; free management at mobile.three.co.uk.