Robocalling telemarketers ignored the Federal Trade Commission's Do Not Call Registry in record numbers in fiscal year 2012. According to the FTC's National Do Not Call Registry Data Book for FY 2012 (PDF), the agency received 3,840,502 consumer complaints about unwanted telemarketing calls in the period, up substantially from the 2,273,516 complaints it fielded in fiscal year 2011.

Telemarketing robocalls are reaching epidemic proportions: complaints to the FTC about robocalls increased from just under 150,000 in October 2011 to 216,338 in March 2012 and remain near that level: 201,699 robocall complaints were received by the agency in September 2012, the most recent month for which figures are available.

Despite the rampant abuse, it still pays to place your telephone numbers in the Do Not Call Registry. To do so, visit the registration page on DoNotCall.gov, enter the numbers you want to block from telemarketers, supply your e-mail address twice, and click Submit to have a confirmation message sent to that address. Then click the link in the confirmation e-mail to add the phone numbers to the registry.

The FTC provides a Complaint Assistant for consumers who would like to register a complaint. You can also report a Do Not Call violator by calling 1-877-FTC-HELP (1-877-382-4357). According to the FTC, the complaints are added to the Computer Sentinel database "available to more than 2,000 civil and criminal law enforcement agencies in the U.S. and abroad," according to an FTC press release dated October 16, 2012.

Another option is to sue the robocallers in small claims court. The people behind the site Kill the Calls claim to have had great success bringing rogue telemarketers into court. The site offers step-by-step instructions for suing Do Not Call violators.

The direct approach to avoiding unwanted callers

Honest telemarketers honor consumer wishes and exclude numbers in the Do Not Call Registry. The organizations ignoring the registry are almost always scammers who make empty promises about relieving people of credit-card and mortgage debt, among other bogus pitches. The crooks are adept at staying one step ahead of law enforcement.

Late last year our home phone number was receiving several of these scam calls each day despite the number having been added to the Do Not Call registry years earlier. It soon reached a point where we fielded three or more robocalls for each legitimate caller. We ultimately changed our landline number as a result of the roboflood.

When the unwanted robocalls started arriving on our iPhones, we were able to keep the scammers at bay without having to change phone numbers. Instead, we use the Do Not Disturb feature on iPhones running iOS 6 to screen incoming calls from numbers we haven't verified beforehand.

The technique works for us because we don't necessarily want to block the calls, we just want to determine whether the call is from a number we know. If it is, we probably want to answer. If it isn't, we'll choose to respond or not the next time we check our incoming-call list.

Android phones make it even easier to screen incoming calls by assigning different ringtones to preapproved and unknown or unapproved numbers.

(Note that all cell service providers let you block specific numbers, although some charge a fee to do so. There are also several free and low-cost apps for iPhones, Android phones, and other phones that promise to create whitelists and blacklists for approved and blocked numbers, respectively, or otherwise block and allow numbers. I prefer the call-screening approach that doesn't require a third party or entail a separate download and installation.)

Screen incoming calls with the iPhone's Do Not Disturb

One way to screen callers on an iPhone is to assign one ringtone to numbers in the phone's contacts and another as the default for all other incoming calls. Then you can answer calls when the first ringtone sounds and screen calls when the second ringtone plays. (You could also record several seconds of silence, upload that file as a non-ringtone, and assign the silent ringtone to numbers you want to "block.")

Unfortunately, the iPhone doesn't let you assign a ringtone to a group of contacts. Your only option is to assign the ringtone one contact at a time. I have yet to find another cell phone that doesn't let you assign a ringtone to a group of contacts.

As an alternative, I add the contacts from whom I want to receive calls to the Favorites list and then activate Do Not Disturb with Favorites chosen as the exception. Then I leave Do Not Disturb on at all times, so calls from any numbers not in Favorites will go directly to voice mail.

Screenshot by Dennis O'Reilly/CNET

I also enable the Repeated Calls option to allow persistent callers from a number not in Favorites to get through on their second attempt within three minutes.

To use Do Not Disturb as a call screener, open the iPhone's Settings app, choose Notifications, and press Do Not Disturb. Switch the Scheduled toggle to ON, set the From time to 12:00 a.m., and set the To time to 11:59 p.m. Press the Allow Calls From option and select Favorites. (Alternatively, you could select All Contacts or another group.) Finally, toggle the Repeated Calls setting to ON.

Now you need only make sure all the numbers you want to receive calls from are in your Favorites list. To add a contact to Favorites, open the contact, scroll to the bottom of the contact screen, and press Add to Favorites. If the option isn't shown, you may have reached your Favorites limit. Simply remove some existing Favorites entries to make room.

Assign ringtones to groups on Android phones

Setting separate ringtones for preferred and non-preferred numbers takes only a few minutes on Android phones. Start by creating a group comprised of the contacts you'll want to respond to right away. in Android version 4, open your Contacts, choose Groups, press the menu button, and select Create.

Screenshot by Dennis O'Reilly/CNET

Give the group a name, and press "Add member." Check the contacts you want to add and press Done. Then press "Group ringtone," select Ringtones, choose a ringtone, and press OK. You can also select a distinctive vibration pattern for the group, if you wish.

Android's Blocking mode lets you prevent all calls from getting through or choose which contacts to receive calls from. To access Blocking mode, go to the home screen and press the main menu button. Press Settings and choose "Blocking mode." Toggle the mode to ON and select "Disable incoming calls," "Disable notifications," "Disable alarm and timer," and/or "Disable LED indicator."

Next, select "Allowed contacts," choose either "All contacts," "Favorites," or "Custom." If you pick the Custom option, you're prompted to add contacts by pressing Add, checking the contacts you want to allow through the block, and pressing Done when they're all selected. Set the time or check Always under "Set time."

Blacklist the numbers used by scammers

After you have received an unwanted call on an Android phone, you can block future calls from that number by selecting the number in the phone's call log (press Phone > Logs), pressing the menu button in the bottom-left corner of the device, and pressing "Add to reject list." Likewise you can block a number in a contact by opening the contact, pressing the menu button, and choosing "Add to reject list."

(Note that these are the options for the Samsung Galaxy S III; other phones and Android versions have different settings for blocking and blacklisting numbers.)

Once again, the iPhone lacks a built-in blacklist or whitelist. As I mentioned above, various iPhone apps promise to create lists of approved and blocked callers. As an alternative to yet-another download and installation, I simply add the number to the iPhone contacts with the name "Scammers" and the date the call was received. Then I assign a distinctive ringtone and vibration pattern to the number so it is easy to identify and ignore.

This lets me track the numbers being used to pitch the scam offers should I ever decide to report the scofflaws. In the last two weeks I have received four calls from one of the numbers (213-710-7325) and two calls from another (458-201-0298). What I would like to do is forward these calls directly to the FTC office that investigates Do Not Call violators. I wonder if there's an app for that.