One of those minor things that would only annoy a pedant like me.

When one books on delta.com, you get this instruction for formatting the phone number:

"Required Phone Number (example: +001-312-3339706)"

That format makes no sense. "00" is the international dialing prefix in use in most countries in the world (not the US.) "+" is the symbol that stands in for whatever the local international dialing prefix might be, and can also be dialed on many cell phone (all GSM, and some CDMA.) So, "+00" would in the US context mean 01100, or, in most of the rest of the world, "0000." The correct format is the "+" followed by the country code (e.g., "+1"), not "+" followed by an international dialing prefix.

And, to further show their ignorance, when you fill in the box labelled "country code" with a "1" for the US, the system saves it as "+001", which of course is not a country code.