Tom Dart wrote that automated assistants such as Cortana and Siri are changing how people speak:

• In the United States voice recognition apps seem to struggle with southern accents and slang.
• People in Australia and India often say they have to fake an American accent to get their smartphones to understand them.
• While voice recognition is getting better…it may not need to. People are adapting themselves to their virtual assistants rather than the other way around.
• Most people have a “telephone voice” – a clearer version of their voice that people use when speaking to strangers or those over the phone.
• But with the hyper-connected world we have today, where people in Texas maybe talking to those in Thailand, people are increasingly using their “telephone voice” during day to day interactions.

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Source: The Guardian