Patty Baxter realized there was a problem. In her 20 years at Metro Guide Publishing in Halifax, Nova Scotia, the office usually hummed with sales calls. Now, it was quiet.

Advertising sales were down and Ms. Baxter identified a reason: Her sales staff, all under age 35, were emailing clients with their pitches, not calling them on the phone.

Younger workers may have mastered technologies that some of their older colleagues have barely heard of, such as photo and video sharing apps Instagram and Vine, but some bosses wish they'd learn a more traditional skill: picking up the phone.

While Millennials -- usually defined as people born between 1981 and the early 2000s -- are rarely far from their smartphones, they grew up with a wider array of communication tools, such as texting and online chatting, and have different expectations for how and when they'd like to be reached. In the workplace, some managers say avoiding the phone in favor of email can hurt business, hinder creativity and delay projects.

Stephanie Shih, 27, says phone calls are an interruption. The brand marketing manager at Paperless Post, a New York-based company that designs online and paper stationery, doesn't have a work phone. Nor do the majority of her co-workers. The company says that not having individual phone lines in open-plan areas protects people from unwanted calls, which can interrupt conversations.

Besides, says Ms. Shih, phones seem 'outdated.' She takes scheduled work calls once or twice a week. 'Even my dentist's office texts me because they know phone calls can be burdensome,' she wrote in an email.

Kevin Castle, a 32-year-old chief technology officer at Technossus, an Irvine, Calif.-based business software company, says unplanned calls are such an annoyance that he usually unplugs his desk phone and stashes it in a cabinet. Calling someone without emailing first can make it seem as though you're prioritizing your needs over theirs, Mr. Castle says. Technossus's staff relies mainly on email to communicate, which helps bridge the time difference between the company's offices in the U.S. and India, he says. He uses Microsoft Lync for instant messaging and video conferencing. Phone calls are his last resort.

But email won't cut it in professions like sales, where personal rapport matters, says Ms. Baxter, age 49. 'You're not selling if you're just asking a question and getting an answer back,' she says.

Earlier this month, a member of her sales team misunderstood an email from a client and anticipated a sale that didn't happen -- a mistake Mr. Baxter says could have been avoided had the employee called the client to begin with.

Since May, she's had Mary Jane Copps, a phone-use consultant in Halifax, Novia Scotia, spend two days a week at the office helping nudge her staff onto the phone. Now, employees keep track of how they contact clients and follow a script when leaving voice mail.

Ms. Copps's training includes role playing that simulates sales calls to help with what she calls 'phone phobia.' 'For many people, it's a lack of confidence that they'll be able to say the right words in the right order in the right amount of time,' she says.

Ms. Copps, 55, whose website is thephonelady.com, charges $1,800 for a full-day workshop. She began working as a phone consultant in 2003 at the encouragement of a friend. She was skeptical at first as she thought phone skills were just common sense.

Jason Nazar, a 34-year-old Santa Monica, Calif.-based technology entrepreneur, says his company has missed out on potential hires because his 20-something employees schedule interviews by email, rather than phoning applicants, which can take longer. 'If you can do something more quickly and more efficiently by using older technology, then do it,' said Mr. Nazar, who is chief executive of Docstoc, a service that helps small businesses manage documents online.

While data traffic on mobile phones nearly doubled, to 1.468 trillion megabytes, between December 2011 and December 2012, the number of minutes spent talking during that period increased by less than 1%, from 2.296 trillion to 2.30 trillion, according to CTIA, a wireless communications trade group.

Businesses aren't giving up on the phone yet. The number of desktop phones shipped to businesses grew by 4.5 % between 2011 and 2012, according to Richard Costello, an analyst at the market research firm International Data Corp. Many new phones allow workers to receive calls, texts, instant messages, transcribed voice mails and more all in one system and access the phone system through their work computers.

Dana Brownlee, a corporate trainer based in Atlanta, says the issue of phone aversion frequently comes up in her projectmanagement training sessions. One of her clients, a manager at a large utility company, recently had to teach his young employee what a dial tone was and explain that desktop phones don't require you to press 'Send.'