pages > http://en.support.wordpress.com/pages/
Comments on all pages and posts on every WordPress blog are enabled by default. This page > Settings > Discussion
Discussion settings is where you set up defaults for comments.
We can also override the default settings and enable or disable future comments on any individual post or page.
Note: By default, new blogs on WordPress.com will have the Discussion hidden. You can reveal it by clicking on Screen Options http://en.support.wordpress.com/screen-options/ on the top right corner of your Admin page, and checking the box that says Discussion so the module is included. http://en.support.wordpress.com/modules/#list-of-modules
Depending on the theme we use when we close comments a phrase like “comments closed” or a similar phrase may appear and if so, it can only be removed by CSS editing after purchasing a custom design upgrade.