Thanks to the thousands of users who click the "Report Spam" button on telemarketers, Google Voice is now able to filter out spam texts, voicemails, and phone calls from unsavory sources.
Every time someone reports a phone number in Google Voice, that data goes straight into Google's data banks for further analysis. And Google runs its own anti-spam tools that add to the knowledge base.
Now, in the same way that Gmail redirects spam into a dedicated folder, Google Voice will keep solicitors from getting their foot in your inbox. If the filter made a mistake, just click "Not Spam."
Google Voice's blog entry says that this spam filter will only get smarter and smarter as it collects more data from users. If you want to give it a spin, just select "Global Spam Filtering" from the Calls tab of the settings page.