they are submitting forms to https://selfsolve.apple.com/deregister-imessage/empty, source says

<!-- Empty JSP created for faking form submission -->

hmmm

It's not as nefarious as you think, I didn't dig into deep enough to know why they are using the empty iframe to submit forms to, but the send button submits an ajax POST request

  main.js:460
  $.ajax({
    type : "POST",
    url : pageContext + pathPrefix + "/turnOffiMessage",
    data:data,
    success : function(data, textStatus, jqXHR) {
    ...