AT&T is a US-based telecoms company, and the second largest provider of mobile services and the largest provider of fixed telephone services in the US.
AT&T Centrex is a central office based telecommunications system. AT&T Centrex typically provides an individual direct dial number per user and does not require on-site common control equipment such as a key system or PBX.
Hypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScript.