Server-side(PHP) validation of phone number that also prevents multiple of same digit, i.e. all 1's

validation.php

function phonenumber($value)
	{
        $areacode = '[2-9]{1}\d{1}\d{1}'; // You might want to specify '2\d\d' (200 to 299)
        $prefix = '[2-9]{1}\d{1}\d{1}';
        $regex = '#^(\('.$areacode.'\)|'.$areacode.')[\s\.-]?'.$prefix.'[\.-]?\d{4}$#';
        if (preg_match($regex, $value))
        {
            // Number now is in a suitable format

            // extract digits -- remove this section to not test repeated pattern
            $digits = preg_replace('#[^\d]+#', '', $value);
            // All numbers equal are rejected
            if (preg_match('#^(\d)\1{9}$#', $digits))
                return false;
            // end of pattern check

            // Otherwise it is accepted
            return true;
        }
        return false; // Not in a recognized format
	}

This is an update to RSFormPro phone validation to be specific to US phone numbers only. I use this as Server-Side validation, along with jQuery validation and a phone mask so user can only input (2xx)2xx-xxxx

Path is typically site\components\com_rsform\helpers\validation.php

Also, can add CSS...
text-transform: uppercase;
JavaScript...
function toUpCase()
{
document.getElementById("first").value=document.getElementById("first").value.toUpperCase();
document.getElementById("last").value=document.getElementById("last").value.toUpperCase();
document.getElementById("email").value=document.getElementById("email").value.toUpperCase();
}

To filter phone input more on mask, in the <script src="/media/system/js/jquery.maskedinput-1.3.js" type="text/javascript"></script> file, you can append to the mask 2:"[2-9]"

...then change the jQuery to $('#phone').mask('(299)299-9999');

This will limit the start of the prefix and leading number to slow random number inputs.