from the plugin description:
PHP GET Variables
Want to use a variable from the PHP GET array? Just use the CF7_GET shortcode. For example, if you want to get the foo parameter from the url http://mysite.com?foo=bar
Enter the following into the “Dynamic Value” input
CF7_GET key=’foo’
Your Content Form 7 Tag will look something like this:
[dynamictext dynamicname “CF7_GET key=’foo'”]
Your form’s dynamicname text input will then be pre-populated with the value of foo, in this case, bar
PHP POST Variables
New in version 1.0.3!
Grab variables from the $_POST array. The shortcode is much like the GET shortcode:
CF7_POST key=’foo’
Your Content Form 7 Tag will look something like this:
[dynamictext dynamicname “CF7_POST key=’foo'”]
