I’ve recently posted a plugin in the WordPress Plugins Directory that adds Campaign Monitor list subscribe functionality to Contact Form 7.

Download it from here:
http://wordpress.org/extend/plugins/contact-form-7-campaignmonitor-addon/

Or read more about it here:
http://www.bettigole.us/published-work/wordpress-contributions/campaign-monitor-addon-for-contact-form-7/

I’ve scrapped my previous version that required core changes to the Contact Form 7 plugin.