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Terry Wendelken called recently with a question that many Vermonters might also have: Why is it sometimes necessary to dial 802 when calling a phone number that's within Vermont?

Wendelken, who makes many calls for his work in Barre, theorized that it's not necessarily based on where he's calling. He's tried phoning towns near Barre, only to hear an automated voice say, "We're sorry. When placing a call in this area, it is now necessary to dial an area code plus the seven-digit number." Moreover, the rules seem different for cellphones than for landlines.

"It drives me freaking nuts," Wendelken fumed. "I must waste a half hour a week, if not more, redialing phone numbers ... What's going on?"

In short, growth and progress. Much of what we take for granted with 21st-century telecommunications, such as unlimited calling and free long distance, are relatively recent developments. Some of the technology we rely on today uses infrastructure and regulations that were created in earlier times.

Vermonters are fiercely proud of their single area code. The cultural cachet of 802 runs so deep that residents sport the stenciled digits on T-shirts, bumper stickers and the butts of their sweatpants. Still, we get irked if we can't order a pizza without dialing those three extra digits, because we assume that any call within the 802 must be local.

To understand the situation, it helps to know why Vermont was assigned its area code in the first place. Though it may seem random that Vermont got 802 while Utah got 801 and South Carolina 803, this disarray of digits was done by design.

First, some background. From the telephone's invention in the 1870s until the mid-1900s, people placed calls by speaking with live operators, who made manual connections through a physical switchboard.

Today's system of assigning area codes, known as the North American Numbering Plan, was developed by AT&T in 1947 to simplify long-distance direct dialing and minimize the human error associated with misinterpretation of the spoken word.

By the time the area-code system was fully implemented in 1951, most calls were placed using rotary dials, which electronically conveyed a series of clicks, indicating which digits the caller was dialing. Lower numbers produced fewer clicks; higher numbers, more clicks. Areas that received the highest volume of calls were assigned area codes that were quicker to dial — that is, had fewer clicks.

As Megan Garber explains in her February 2014 piece in the Atlantic, titled "Our Numbered Days: The Evolution of the Area Code," to ensure that early, primitive computers accurately recognized the number of clicks, AT&T engineers created a system that placed either a 0 or a 1 in the middle of each area code. Zero indicated that the state had only one area code, and 1 indicated it had more than one.

Because New York City had the highest call volume in those days and was located in a state with multiple area codes, it was assigned the easiest area code to dial: 212. Los Angeles, with the second-highest volume, got 213; and Chicago, 312. Vermont, with its comparatively low call volume and single area code, got 802.

To further minimize errors, codes that resemble each other were assigned to geographically distant places; hence Utah's 801 and Vermont's 802.

Fast-forward to the 21st century: Why don't all calls to and from 802 connect without using the area code? Rob Koester is vice president of product management at Consolidated Communications, the company that acquired FairPoint Communications in July 2017.

As Koester explained, two circumstances require a customer to dial a 10-digit versus a seven-digit number. The first occurs primarily in large populations centers that are running out of phone numbers. Once a new area code is assigned in that area, he explained, everyone must switch to 10-digit dialing, regardless of whether they're calling from a landline or a cellphone.

That's not yet the case in Vermont. Landline callers in the Green Mountain State sometimes must dial 802, Koester said, because of how the network was built and subdivided geographically.

In the early days of telephony, each phone exchange — that is, the first three digits of a seven-digit number — was assigned to a specific "calling scope," or geographic area, within which all calls were considered local. In those days, customers could call other exchanges within their own calling scope, such as Burlington to Winooski, for free. But calling a different calling scope, such as Burlington to Brattleboro, incurred a long-distance charge.

"The seven-digit dialing is a remnant of those local calling scopes," Koester explained. "Any place that was traditionally considered a local call is still a seven-digit dial."

So, how do Vermonters who've never used a rotary phone or incurred a long-distance charge know whether a call requires seven digits or 10? According to Koester, local calling scopes were usually, though not always, laid out according to city and town boundaries. Generally speaking, neighboring exchanges are still considered "local."

Things got more complicated when cellphone companies arrived, because they laid out their cellular networks differently and have greater flexibility in call-scope design. In addition, wireless providers aren't regulated by local public utilities commissions in the way that landline companies are.

Further muddying the waters is when people use cellphones to call landlines, and vice versa. In those cases, Koester said, connectivity rules depend upon where and how the two networks interconnect. In short, don't ask.

Still irked about having to dial 802 when calling within Vermont? Get used to it. As Koester pointed out, seven-digit dialing is "a dying breed" in most of the country. Just be grateful that Vermont isn't at risk of depleting its precious supply of 802 phone numbers anytime soon.