It is indeed possible to control the entire network, and do anything an cellphone operator can do. Now, at least three software companies have released personal security software for emerging smartphones, girding for a new wave of phone viruses and Captain Crunch-style tricks. F-Secure is one such firm, selling antivirus and encryption software for smartphone operating systems made by Palm, Microsoft and the Symbian platform common in Europe.

Thus far, there have been no publicized reports of phone hacking or viruses, although viruses have attacked handhelds running the Palm operating system. Microsoft predicts deviant code will soon emerge for handhelds running its Pocket PC software. Both operating systems are expected to be used increasingly in smartphones. A virus is a piece of malevolent code that self-replicates, while a Trojan horse does not but can be just as destructive. The pranks in Europe and Japan created virus-like havoc, but did not propagate like a full-fledged virus. For virus writers who crave notoriety by wreaking maximum havoc, there are still too few smartphones, and no widespread software platform to attack.

That is starting to change. Until recently, cell phone operating systems were "closed," unable to download software. But new smartphones -- like the Nokia Communicator, Handspring's Treo, Motorola's Java Phone and Mitsubishi's Trium-Mondo -- are open to such third-party downloads. At the same time, software developers' tools available for designers of such programs as games and currency converters can also be used to create malicious applications.

It's possible for anyone to make custom software for this platform. Teens can download development tools and write their own software. It's these third-party programs that worry experts. If one is disguised as a Trojan horse, an infected phone could make some calls on its own. The website "virus.cyberspace.sk" posted a bulletin exhorting readers to create phone viruses. It stated, "We are starting Cell Phone Virus Challenge. Any contribution welcomed.". The page has since been taken down.

Soon, mobile phone owners will be obliged to install security software like "personal firewalls" that used to be reserved for Internet servers. That's where things are going. It's the same threat as the wired world: people posing as you, stealing your identity or your personal information, and using your information for malicious purposes. Cell phone users can avoid this, of course, by sticking with their old "dumb" phones.

There are trade-offs. Do you want a phone with a tiny monochrome screen where you can only make phone calls? That's much more secure.