Been working on this and here's what I've found.  In the United States and Canada when we want to dial a number we ONLY use a country code if we are calling outside of North America.  Maybe Mexico, never tried it.  For example, I want to call Toronto, ON from Phoenix, AZ.  Typically I would dial 909 555 1212, no country code needed even though I'm calling Canada.  

Now, back in the old days lets say I wanted to call my dad in Ohio, he lived outside cleveland with the area code 216.  I'd dial 1 216 555 1212 and the number would go through, we didn't call that a country.  So I figured I'd try that w/the 12165551212 and the system denied it.  

So I dug a little more.  I noticed it said numbers or digits only.  But it kept referencing this + in the error box.  So I tried +12165551212 and lo and behold it works.  So all my members have to type + 1 then area code and then number.  

If the system wants a + then we need to code the + to be automatic and in the background, not something the member needs to add in as here in the US & Canada I can tell you none of us think of a phone number as + 1 area code number.  The 1 we can live with, the + is boonex overkill.