1.) Go get the "Contact Form 7" plug-in and install it.
2.) Create a form as discribed egg. [contact-form 1 "Call back form"].
3.) Create a new post. In that post you put the Code egg. [contact-form 1 "Call back form"]. Now create a new Category "forms" - that's just for you to exclude further on this category from your published posts.
4.) Go to administation panel and find out what is the post/page-id egg. it's "96"
5.) Open you sidebar.php and include their the following code:
<?php query_posts('p=96'); if(have_posts()) : the_post(); ?>
<?php the_content(); ?>
<?php endif; ?>
6.) Save and upload. Finish!
Now you can easy change settings etc. of the contact form over the backend.