function isPhoneValid(field) {
    phone = field.value;
    numDigits = 0;
    valid=true;
    foundFirst=false; 
    if(phone!=""){
        i=0;
        while(i<phone.length){
            ch = phone.charAt(i);
            if (ch!=" " && ch!="-"){
                if(ch>="0" && ch<="9"){
                    if (foundFirst || ch!="1") {
                        numDigits++;
                    }
                    foundFirst = true;
                } else {
                    valid=false;
                    break;
                }
            }
            i++;
        }   
        if(numDigits!=10) {
            valid=false;
        }   
    }   
    if (!valid){
        alert("The phone number of \""+phone+"\" is invalid.\nPlease enter a phone number in the form of 800-555-5555");
        field.focus();
    }
    return valid;
}