I have the same problem with people from El Salvador. I certainly hope someone from Apple fixes this. This is one of the advantages of using a PIN number with international numbers.
So, it's not only a problem in Mexico.
And here I was beginning to wonder, who in their right mind thought that would be a great idea prepend the 1 before the area code when calling from outside the country.
So anyway, this problem goes even deeper than what you guys describe.
Because you have / can only add the one when calling from outside the country. In other words when you try to call a mexican cell phone from withing Mexico you cannot store the number as +52 1 (614) xxx-xxxx as you would normally do and then call that, like it works in any other sane country.
Because calling from within you have to omit the 1.
SMS need to be send to the number without the 1, even from outside Mexico, otherwise they don't work. WhatsApp and iMsg only add to the mess, since it seems that some people register their cell# with whattsapp with the 1 added, others without. Believe me I, I registered multiple cells with Whattsapp in Mex. and since SMS sending does not seem to work from the US whattsapp account in any case, you have to get a call and there is no clear indication as to whether you're supposed to prepend the 1 or not. It seems to work regardless.
In other words, you need to store both numbers for every contact you have.
Which is why by now, I have almost all our contacts with 2 numbers listed, mobile without the 1, and 'mobile MX' with the 1 prepended.
Has anyone filed a bug report with Apple for that? Since that problem seems to exist in more than one country that would be the best route to go.
They have to build something very deeply into the contact system that recognizes when it's a number from any of those countries and automaticlly prepend the 1 when dialing, but leave it out when any other app asks for it.
I'm willing to look into building a cydia tweak for it for my own mental well-being since this is driving me crazy, but that doesn't help a lot of people...