You can make a auto pop up form using contact form 7. Although it will not be worked by it self. you need to customize and apply my another trick. install a plugin popup maker. Then go the plugin setting color, text etc. Now paste the short-code on a page where the popup will be displayed.
Now go to Contact for 7 plugin option and copy the short code of it and put it into popup maker form where you first created a popup. It means contact form 7 will be displayed by popup maker plugin. you may create custom field like mobile, phone, subject as you generally get in contact form 7.