The New York attorney general is probing whether three major Internet providers could be short-changing consumers by charging them for faster broadband speeds and failing to deliver the speeds being advertised, according to documents seen by Reuters. The letters, which were sent on Friday to executives at Verizon Communications Inc, Cablevision Systems Corp and Time Warner Cable Inc, ask each company to provide copies of all the disclosures they have made to customers, as well as copies of any testing they may have done to study their Internet speeds.