AT&T also spent enormous money & efforts in Lobbying, which made it gain monopolistic powers in telephone industry.
However, these benefits declined & it failed because :
a. The comprehensive telephone equipments & services company was split in 1980s by government litigation, into many local phone companies, a long distance company & a phone equipment company
This diluted the power of company. But it also broke the monotony and encouraged diversification, in terms of variety of payment plans & telephone equipments design & colours.
b. Afterwards, there were innovations in technology for providing telephone services from wires to microwave & satellite transmissions, specially with growth in cellular phone systems.
They were unable to catch upto these technically upgrading innovations, which made them loose monopoly power.
c. Due to industrial transformations, a wave of government deregulation also started, which liberated entry of firms & weakened their position.