Stories abound of used cellphones found still containing personal and sensitive information from their former owners, from handsets donated to charity, sent off to recycling services, sold off on eBay, given away to roommates, or simply left behind in the back seat of a taxi cab. If you use your cellphone to carry e-mails and company files from work or personal photos that you'd rather not fall into strange hands, then its worth taking steps to wipe your phone clean before bidding it farewell.

This is just a precaution, not a problem you should find yourself losing sleep over. There is no crime wave in effect, no sprees of gangs collecting used cellphones to mine them for credit card numbers, nude photos, or corporate secrets, but it is a mistake commonly made, a step most people never think to take, and like leaving your car unlocked at the airport or counting your money while walking down the street, you're just asking for trouble if you ignore it.

The real concern is with "smartphones", handsets like the popular Treo, MotoQ and Blackberries, ones that are a combination of a phone with a personal organizer and can be synchronized with a desktop computer to store spreadsheets, word files, memos, and powerpoint presentations. These phones can often take memory cards (which should never be included with a phone when you sell/give it away), but its the built-in "flash" memory that always stays from the phone and should be erased.

Most handsets are designed with a secret sefl-destruct feature, a hidden series of steps that you can take to "hard reset" or "wipe clean" your phone's built-in memory. Every model is different and to discover how to wipe your phone clean you'll need to refer to its manual. If you've lost the manual, you can go to the manufactuer's website and download a copy.

Palm Treo owners will find Hard Reset directions here.

Blackberry users will find device wipe directions here.

For other brands you can check with WirelessRecycling's online data eraser tool. Choose your brand from the drop down menu and then download and follow the instructions.

But what if you've lost your cellphone?

If you've left your Treo or Blackberry behind on a taxi's backseat or inside a subway car, it is possible to have a special wireless SMS message to your phone to activate a lock down feature that prevents its information from being accessed.

If this happens to you, contact your cellphone carrier or the manufactuer and they might be able to perform this for you (no guarantees I'm afraid).

There are a few companies that offer this as a third-party service, but only to corporations and organizations with a fleet or more than ten smartphones. Their services are offered as a security package that you subscribe to.

MotionApps' mSafe works on Treo Smartphones and offers a free 5-day full, trial version of the program for download. You have to install the software onto your phone before you lose it in order to use the feature.

Trust Digital offers a remote security service for large companies that can remotely wipe all popular brands of smartphones.

What about broken phones?

Whether you dropped your cell phone in the toilet (#1 most common cellphone accident) or watched it smash against the sidewalk one time too many, you may have a handset that no longer works. You can't erase its memory, but the sensitive data may still be in the phone. Should you be worried?

Although its highly, highly unlikely that someone is going to try to hack into a dead phone, I admit it is technically possible and the rule is that if someone is committed to accessing your information, they will go to great lengths to do so.

It's time to bring out the sledgehammer. Physically damaging a phone beyond repair is the only sure way to erase any memory stored in it. Note: Remove the battery first! Or do I need to remind you what a lithium-ion battery is capable of? And wear eye protection.

This is also the solution for those with paranoid-level senmsitive information. If the e-mails or photos on your phone are so incriminating as to destroy your life should they ever surface, don't trust a memory wipe and go for the sledgehammer instead.

A friend of mine, who had just gotten out of jail, passed on this lesson to me - "A secret is only a secret if you don't tell anybody". He learned the hard way, don't let that be you.