Officials at Facebook, Google and Twitter (all reached first by e-mail) say their users prefer to go online, finding it more pleasant and efficient than wading through a phone tree. But what about other business matters? What if, say, a prospective investor wants to call?

“If people need to get ahold of us, they definitely have sources inside,” said Derek Stewart, the finance director of Foursquare, whose personal cellphone has been mistaken for the company’s main office line. In Foursquare’s offices in New York, phone calls are considered a distraction to the developers and are conducted away from the main work area, in British-style red phone booths, the company’s spokeswoman said, explaining that calls are not part of developer culture.

Still, others see a social cost to this change, a deepening of the digital divide.

“The phone users are getting left out,” said Mari Smith, a consultant who trains businesses in how best to use social media. She should know. Because her consulting company lists an 800 number, frustrated people call all the time, looking for help with their Facebook accounts. She eventually adjusted her phone message to callers to explain that she does not provide technical support for Facebook.

“I just got bombarded,” she said. “They’re just so desperate to reach a real human being.”

Ms. Smith said she believed that large Internet companies might someday return to phones to set themselves apart from competitors. “The ability to call up and get a real human being — the companies who can do that and go back to basics are really the ones that will be winning out and humanizing their brand,” she said.

But for now, some people still feel frozen out when they pick up the phone.

Gabriel McKean, for example, was eager to start using Twitter. His 5-year-old daughter has a rare and painful genetic condition that turns her body’s soft tissue to bone, and the McKeans, who live in Bellevue, Ohio, started a Twitter account for “Ali’s Army” to raise awareness of her disease.

But the account was suspended in a matter of hours — Mr. McKean’s repeated posts of the family’s Web site were quickly flagged by Twitter’s systems as spam.

Upset and confused, he searched Twitter.com for a phone number, but found nothing. He sent an e-mail, but received only automated replies filled with jargon that confused him further. Without other options, he had no choice but to wait for someone to reinstate his account over e-mail.