ATT Southern California Customer Service Numbers Home» ATT» ATT Southern California Call at 866-577-7726Mountain Square, 320 S Mountain Ave, Upland, CA 91786, United StatesDirections: Follow the directions to locate ATT Southern CaliforniaLocations Near You: Find nearby locations of ATT Southern CaliforniaGeneral customer convenience numbers: 800-288-2020New consumer attandant customer convenience number: 888-715-3291 Additional Contact Number: 866-346-1168Basic OverviewATT is an American international telecommunication industry inaugurated in the year of 1885. It is listed among the globe's leading telecom industry and counted among the 2nd biggest distributor of mobile telephone facilities and biggest issuer of fixed telephone services across USA. For over 34 years of experience, the telecom industry invents cutting-edge products and services that simplify complex life which constitutes super-fast internet and unlimited data plans.ATT Southern California is one of superior units of ATT company. ATT Southern California department is eminent for quality and dependable delivery of the Habitat and professional commodities and assistance to users of southern California population. ATT Southern California boundless span of assistance envelopes each personal and business areas of California society. For the merits of users of California province, ATT Southern California has positioned number of stockpile over state counties so that patrons of corporation take entire provision of assistance that has ben put outwarded by astounding ATT Southern California.