Here are two screen caps from a web application I just had to use to pay a tuition bill.
Presumably developed by professionals, and no doubt it is expensive. Assuming the usual for academic IT applications, an absolute fortune. Here are the terms-and-conditions to which one agrees.
Standards of usability, anyone? Why am I in this end of the business?
As an extra bonus, I tried putting my telephone number into the box using my preferred form of 123.456.1234. It rejected it as invalid, but didn’t suggest what would be a valid formula.
It turns out there are several ways to program in a user-friendly test for telephone numbers. There are several ways outlined here, the simplest of which is to take the user-entered string and strip out all non-numeric characters. If you’ve got seven numbers left, it’s a US telephone number. Then, when you display it, format it however you like.
Or this. If you’re a fan of the famous e-mail address regex, you’ll appreciate:
^(?:(?:\+?1\s*(?:[.-]\s*)?)?(?:\(\s*([2-9]1[02-9]|[2-9][02-8]1|[2-9][02-8][02-9])\s*\)|([2-9]1[02-9]|[2-9][02-8]1|[2-9][02-8][02-9]))\s*(?:[.-]\s*)?)?([2-9]1[02-9]|[2-9][02-9]1|[2-9][02-9]{2})\s*(?:[.-]\s*)?([0-9]{4})(?:\s*(?:#|x\.?|ext\.?|extension)\s*(\d+))?$