For the past 50 years or so people have mostly had 7 digits, but in some places just dialing the last 5 numbers was sufficient – omitting the prefix. The first 2 numbers represented a name such as "BRoadway," "FLeetwood," "EMpire," "PLaza," or such and were optional in many areas.
Then came the time when we had to dial all 7 digits, and now, many people have to dial 10 digits - even for a "local" call. Of course, with cell phones that often is just part of the stored number or the contact and we don’t even think of it. Actually, we frequently dial people from our favorites list or our contact directory without ever entering the actual digits of their phone number.
If we don't live with multiple area codes in our immediate area or with different area codes within an hour's drive, we likely don't think too much about the need to request or write down the area code when noting a phone number. We just assume it’s the same as ours.
As long as we don’t travel or venture to another area, or order anything online or over the phone, not supplying the area code and just assuming that people we are contacting or interacting with know what to dial to reach us, it’s OK. However, this is becoming less the case.
Now that people are able to take their cell phone numbers with them when they move (not to mention just taking our cellphones with us when we go to another city for business), it's not unusual to see an area code from several states away that we must dial just to talk to a neighbor or associate.
Hardly anyone pays long distance charges anymore so having a non-local area code is not an issue. Also, the need for a toll-free number (800, 877, 866, 855, etc.) is largely unnecessary for the same reason that cell-phone and many land line calling plans include long distance at no additional charge.
We just need to make sure to give out all 10 digits of our number when handing it out or leaving a callback (just to make sure) and request all 10 digits when we are getting a number from someone even if we are relatively certain the area code is a local one. We also need to verify that our complete 10-digit number, including the area code, is on our business card. We might work with people who share our area code, but there’s always someone from outside our area that we going to meet. That’s when having the area code printed on the card becomes important.
We can't afford to lose contact with someone – whether it’s a phone call or a text message - just because we are missing a 3-digit area code from our business card, assessment or estimate form, or letterhead, or assume incorrectly that it's the same as ours.