// Declaring required variables
var digits = "0123456789";
// non-digit characters which are allowed in phone numbers
var phoneNumberDelimiters = "()- ";
// characters which are allowed in international phone numbers
// (a leading + is OK)
var validWorldPhoneChars = phoneNumberDelimiters + "+";
// Minimum no of digits in an international phone no.
var minDigitsInIPhoneNumber = 10;

function isInteger(s)
{   var i;
    for (i = 0; i < s.length; i++)
    {
        // Check that current character is number.
        var c = s.charAt(i);
        if (((c < "0") || (c > "9"))) return false;
    }
    // All characters are numbers.
    return true;
}

function stripCharsInBag(s, bag)
{   var i;
    var returnString = "";
    // Search through string's characters one by one.
    // If character is not in bag, append to returnString.
    for (i = 0; i < s.length; i++)
    {
        // Check that current character isn't whitespace.
        var c = s.charAt(i);
        if (bag.indexOf(c) == -1) returnString += c;
    }
    return returnString;
}

function checkInternationalPhone(strPhone) {

    s = stripCharsInBag(strPhone,validWorldPhoneChars);

    return (isInteger(s) && s.length >= minDigitsInIPhoneNumber);
}

// param Phone - html input object
function validatePhoneNo(Phone) {
    /*
	if(Phone.value=="") {
        alert("Please Enter a Phone Number");
        Phone.value="";
        Phone.focus();
        return false;
    }
    */
	
	if(Phone.value=="") return true;
    if (checkInternationalPhone(Phone.value)==false){
        alert("Please Enter a Valid Phone Number");
        Phone.value="";
        Phone.focus();
        return false;
    }

    return true;
}