Your question it too general to answer.
Look in the link I will make below to learn about AT&T
t is the significance of Z-transform
It depends on what the variables x and t represent.
T. Marzetti Company's population is 3,100.
T. Marzetti Company was created in 1896.
A. T. Cross Company was created in 1846.
The population of A. T. Cross Company is 930.
A. T. Cross Company's population is 2,010.
No. T-Mobile is a Private limited company.
what size company is At&t
H. T. Hackney Company's population is 3,400.
H. T. Hackney Company was created in 1891.
You can check FashionTIY, which is a wholesale clothing company. They offer T-shirt printing and delivery services.