You should be able to refer to whether the email checkbox was checked or not with:
WA_getSavedFormValue("CheckoutWizard_Sharp_Default","emailList");
and then the email address would be:
WA_getSavedFormValue("CheckoutWizard_Sharp_Default","Email_Address")
and the name would be:
WA_getSavedFormValue("CheckoutWizard_Sharp_Default","First_Name")
WA_getSavedFormValue("CheckoutWizard_Sharp_Default","Last_Name")
So your code might look like:
<?php
if (WA_getSavedFormValue("CheckoutWizard_Sharp_Default","emailList")) {
$theEmail = WA_getSavedFormValue("CheckoutWizard_Sharp_Default","Email_Address");
$theFirstName = WA_getSavedFormValue("CheckoutWizard_Sharp_Default","First_Name");
$theLastName = WA_getSavedFormValue("CheckoutWizard_Sharp_Default","Last_Name");
$theFullName = $theFirstName . " " . $theLastName;
// constant contact code here
}
?>