If your teachers were anything like mine, the difference between "can" and "may" has been ground into you permanently. After many times of asking "Can I go to the bathroom?" instead of "May I go to the bathroom?" I finally internalized the distinction between the two words: "can" implies possibility, while "may" implies permission.
This rule is a bit old-fashioned, and I'm not even sure parents or teachers even bother with it anymore. Today, most people only pull out "may" when they want to come across as ultra-polite. For instance, when a timid salesperson talks to a prospect about their business, they might phrase their discovery questions like so:
"May I ask about last quarter's results?"
"May I inquire after your team's organizational structure?"
"May I ask when the last time you invested in this area was?"
Sounds polite, right? For prospects who are extremely courteous, this type of language might be a turn on. But in the majority of cases, using "may" actually hurts a salesperson's approach.
As Wendy Weiss points out in this article, prefacing questions with "may" can make the salesperson seem weak.
"Do not say: 'May I ask you a question?' This gives up your control of the conversation," Weiss writes. "With this question you are asking permission, and you don't need permission to ask questions."
By the nature of the prospect picking up the phone and remaining on the line, you have their permission to speak and ask questions. If there's ever a question a buyer would prefer not to answer, they'll tell you so. But there's no need to make your speech more convoluted in the meantime.
Instead of starting with "may," Weiss recommends simply launching into your question with "who," "what," "why," or "how." Here are the sample phrases above once more, this time without "may:"
"How were last quarter's results?"
"What is your team's organizational structure like?"
"When was the last time you invested in this area?"
Now the questions are much more direct, and the salesperson sounds more self-assured. And I think you'd be hard-pressed to find someone who'd consider the phrasing rude.
Your third grade teacher might disapprove, but your prospects likely won't. When asking questions of buyers, skip the "may" and simply dive in.
Verdict: not recommended.