Michael Porter: Five Forces:
(1) The threat of the entry of new competitors: Low. Because new entries do have to invest lots of money to facilities so than they services can cover wide range in order to compete with the exited companies, there are several companies that can entry to this industry at ease. It is obviously that the threat of the new competitors is low.
Considering I-phone, with the new technology, it is possible that one day portable laptop can be as small as mobile phone. If at that time Wi-Fi is spread around the whole country and everyone can have access to Wi-Fi everywhere, customers can communicate with each other online. It could be but may take a long time to be a big threat to the industry.
(3) The threat of competitive rivalry: Moderate. In the United States, the majority market shares are occupied by four big companies and AT&T is one of them. Even though competition among the four companies is intensive, the whole market competition is not as munch intensive as other industries such as software industry in which there are more than thousands companies.
(4) The bargaining power of customers: Low. There are only four major companies in a country with hundreds of millions population, and the mobile phone is indispensable for everyone. Considering the low demand with high need, the bargaining power of customers is low.
(5) The bargaining power of suppliers: Low.