The moment you think you’ve lost your wallet, you get that panicky feeling. All of your cash, your ID, and your credit cards are suddenly gone. Your range of options is dramatically limited. You might be stranded somewhere, unable to get home or into the club where your friends are. You can’t buy food, lodging or transportation. It’s scary, frustrating, maddening, and the clean-up is a mess: you have to contact your bank, your credit card companies, your air travel and other loyalty card providers. You need a new driver’s license and perhaps social security card. What were all of those cards in your wallet? How do you reach all of those providers? Thank god you have your cell phone.

But given the choice between have my wallet or my cell phone stolen, I’d much rather lose the wallet.

My cell phone has all of the email conversations between me and my friends and my clients. There’s also a phone directory of everyone I know, a calendar with my birthday, their birthdays, and everywhere I am planning on being (or have been) for months. It would be easy to impersonate me on the phone, by email, and in all of the online communities in which I participate: email, Facebook, LinkedIn, Twitter. You could ruin my reputation, extort money, and victimize anyone I know.

There’s also confidential client data — presentations and meeting notes, recordings,and photos. All of that is in addition to the thief’s ability to access to my bank, financial institutions, PayPal, investment firm, and Mint.Com.

Cleaning up after having your wallet stolen is a cakewalk compared to the mess you’re in if your phone is compromised. Yet people are way more casual about leaving their phone laying around than their wallet.

Part of the reason for this is that the function of a wallet has remained relatively constant, while the function of a phone has dramatically increased in scope. Even though it’s a now a GPS navigation system, financial terminal, email client, Internet browser, hard drive, camera, media player and social media device, we still call it a “phone.” Our attitude about phones hasn’t kept up with the phone’s increasingly important role.  The truth is, if I had to eliminate one function of my phone, I would do without the part where you talk to people.

Even if you’ve been slow to realize how important your phone is, criminals have not. Antivirus firm McAfee reports that last quarter mobile device malware was up a whopping 46%, while other threats we down overall. The problem is only going to get worse as phone functionality increases. This year near-field communication chips are being added to phones which literally turn them into wallets, meaning you can lose your phone and wallet simultaneously.

Virus attacks on your desktop computer are becoming passe, with most users aware of the threat and using a range of very good free and low-cost AV tools. On your phone, you’ve had fewer options. But that’s changing as phone manufacturers and software developers recognize this threat.

The first line of defense is to use your phone’s built-in password security. Most people don’t turn this feature on because it’s a nuisance to enter a password every time you pick up your phone to use it. Unless your phone is stolen by the NSA, this feature does a great job of protecting information stored in your phone itself, although it does nothing about data or documents stored on your phone’s removable memory card.

To encrypt passwords and other sensitive data that you carry around with you, there are specialized applications like OISafe. Programs like WaveSecure can help you track a missing phone, backup up the data on it, and remote wipe the memory on command.

Those applications are great if you know that your phone has gone missing, but the far greater threat is malware which can steal the data off your phone while you’re using at it. While there hasn’t yet been a wide-reaching virus attach on mobile devices, it’s just a matter of time as tablets and phones replace laptops as people’s primary mobile device. This past year has seen Norton, McAfee, AVG and dozens of smaller companies release smartphone security applications, many of them not very good. (Lookout Mobile Security is a standout, featuring anti-virus, lost phone tracking, remote backup and remote wiping.) Expect to see an arms race on mobile devices play out in a way similar to the way it did on the desktop, only at an accelerated rate. (Hackers and AV companies have, after all, learned a lot from the desktop wars and will be applying it to the battle for mobile security.)

So, you’ve been warned. If you haven’t taken the time to set the lock code on your phone, do it now. And think about installing an anti-virus application and a remote-wipe function. It’s simple to do now, and impossible to do when you realize you really need it.