Insert Multiple Post with Same Publish Button

This should be possible, but it will take some work. As you found out, at the end of the wp_insert_post function, there is a hook save_post_{$post->post_type}, which you can do to additional stuff when a post with a certain custom post type is created. However, if you use this hook to create additional posts, the hook will be encountered again and you end up in an infinite loop. So, you must make sure that the hook is not used the second time. It goes like this:

add_action ('save_post_yourcustompostname', 'wpse359582_make_three_posts');
function wpse359582_make_three_posts ($post_ID, $post, $update) {
  // remove the hook so it won't be called with upcoming calls to wp_insert_post
  remove_action ('save_post_yourcustompostname', 'wpse359582_make_three_posts');
  // make three copies
  $post1 = $post;
  $post2 = $post;
  $post3 = $post;
  // Now manipulate the three posts so each has a unique IMEI number
  ....
  // update the original post
  wp_update_post ($post1);
  // remove the id from the other two posts so WP will create new ones
  $post2['ID'] = 0;
  $post3['ID'] = 0;
  wp_insert_post ($post2);
  wp_insert_post ($post3);
  // put the hook back in place
  add_action ('save_post_yourcustompostname', 'wpse359582_make_three_posts');
  }