The new service (which is currently only available to users in the U.S.) will provide users with SMS alerts for things like new users joining or leaving a blog, a change in theme and an update in privacy settings.
Users that pay $20 a year can also get access to additional features, including:
The ability to protect your blog with a two-step login process. You'll get a text message on your phone when you log in to your dashboard that contains a passcode that must be entered before you gain access to your blog.
Text notifications when you receive a new comment, plus the ability to approve or delete comments and the ability to send in your own comment replies.
Get notified when a new post is published to your blog.
The ability to publish quick updates to your blog instantly.
If you have an iPhone, Android or BlackBerry device, you can probably comfortably avoid the need to spend $20 per year, since the various official WordPress mobile apps offer the same features as the new text messaging options, plus the ability to post photos and videos and edit existing posts or draft new ones.
We think it's pretty cool that you can manage your comments via SMS but we're not really sure that such a feature is worth $20 per year. If you just want to be able to post to your WordPress.com blog via SMS and don't care about the extra security options or the ability to approve/delete comments, you can use a free service like Ping.fm to post short quips or remarks to your blog.