It's hard to find people who don't rely on mobile phones for personal or business use. According to the Cellular Telecommunications and Internet Association (CTIA), more than 180 million wireless subscribers exist nationwide. This number grew by 13.7 percent since 2004 and the wireless minutes used rose to more than 1 trillion that year, a 33 percent increase from 2003.

Although the statistics don't show the number of public safety users, the existence of wireless services that enhance public safety communications show carriers' interest in that market base. At Nextel Communications, for instance, Russell Wilkerson, director of corporate communications, says the company "works closely" with the public safety community, which includes users of Nextel's differentiated push-to-talk instantaneous walkie-talkie service.

The downside to all this is the same people who flood e-mail inboxes with advertisements for prescription drugs, loan services and pornography have begun targeting mobile phones. Says Eric Lofdahl, vice president of engineering at Wireless Services Corp., which manages the data networks transporting text messages for several North American carriers including Nextel, "We are starting to see spam aimed at trying to sell cell phone accessories for the particular cell phones each carrier offers." Spammers don't appear to target particular demographics; Wilkerson says their strategy instead centers on volume.

Lofdahl says most spam originates from a PC, just as e-mail spam does. "Since the Federal Communications Commission (FCC) assigned blocks of phone numbers to carriers, those numbers are targeted via carrier Web sites, old paging sources and sometimes over SMTP pathways. In one case, spammers in Egypt used the SS7 telecommunications network infrastructure." Wilkerson adds, "Spammers use a variety of methods and are always modifying their techniques to try and outflank filtering technologies."

"There is no difference between the ways spam gets to wired versus wireless devices," says Jon Lei, president and CEO of Roaming Messenger Inc. "The Internet and the telephone system are open networks, meaning you don't need permission to send e-mails and dial numbers. Cell phones have e-mail addresses, so just as spammers scan Web site registers for certain Internet Service Provider-hosted e-mail addresses, they can simply guess the 10-digit phone number that identifies a cell phone's e-mail."

Wireless Services estimates 43 percent of all U.S. mobile phone messages are spam, a 25-percent increase over the last year, although Lofdahl notes that wireless consumers are unaware of the increase because Wireless Services' technology blocks spam before it reaches handsets. Nextel itself estimates that up to 40 to 60 percent of all messages hitting its network consist of spam. Wilkerson says the volume continues to increase.

In Europe, the problem is worse. The University of St. Gallen (Switzerland), together with Swiss telecommunications network service provider, bmd wireless, recently released a study that showed 80 percent of 1,659 surveyed mobile consumers had received unsolicited messages and 83 percent of the 154 industry respondents thought mobile spam would be a critical issue within the next year or two.

U.S. industry insiders share that opinion. "We have seen a steady growth of spamming attacks and volumes as part of a multi-year trend," says Lofdahl. "It has gotten noticeably worse over the last 12 months. We don't have good industry-wide numbers; however, from talking to major and some regional carriers, we see spam increasing at around 10 percent a month."

For most consumers, the only evidence of spam delivery is anecdotal. For those who actually receive a mobile spam message, it's a nuisance. Business users may notice a loss in productivity and related costs (although Lofdahl says that no estimate of actual costs exists, but it is probably a low figure).

For public safety consumers, though, spam could disrupt mission-critical communications. Law enforcement officers from different agencies use mobile phones when they don't have radio interoperability, as some did following the Atlanta courthouse shooting in March.

Lei says text messages' static nature is another inherent problem. "You need a way to make sure the recipient sees the message and then takes action or makes a decision," he explains. "But if the message is buried under 10 or 20 messages — a bomb threat surrounded by prescription drug ads — it will be more easily lost."

Before mobile spam reached these proportions, wireless carriers, who bill per message, actually stood to make money from spam delivery. Because of the nuisance factor, however, many carriers seek to end the problem: the University of St. Gallen study showed that, with spam-laden consumers more likely to switch carriers than phone numbers, both consumer and industry respondents believed responsibility for fixing the problem lay squarely with the carriers.

"Spam degrades the customer experience, so we are focused on preventing it," Wilkerson says. "There is no economic value in allowing spam onto your network because the cost of a call to customer care from an unhappy recipient is far more expensive than the potential revenue generated from messages. Nextel's goal is to provide customers with the best services they require, not unsolicited services that create inconveniences and added costs."

Both Wilkerson and Lofdahl stress that all customers, including those in public safety, should notify carriers if and when they do receive spam. "This information will help us better track the situation and more effectively respond," says Wilkerson. "Also, we monitor customer care calls to measure the effectiveness of our systems and our responses."

Wireless Services has built one of the only solutions that specifically combats mobile spam in the United States. "We help carriers avoid the real costs of delivery and customer dissatisfaction by filtering the spam out at the network edge, before it gets delivered," says Lofdahl. "Our anti-spam software addresses multiple layers of the mobile network, seeking patterns specific to mobile devices, and ensures rapid delivery of messages. Many e-mail-based spam solutions miss wireless-targeted spam and cause delivery latency, which may be acceptable for e-mail, but not when a carrier is delivering mission-critical, time-sensitive messages."

Wireless Services' solution uses most standard techniques to identify and block spam, including IP address blocking, white and black lists, and Bayesian probability, among others. "However," says Lofdahl, "what sets us apart is that we look at all sources that can provide information spammers can use, such as carriers' Web sites, and aggregate the information collected."

Where the solution is deployed on the various network layers depends on the carriers themselves. Large carriers may have the facilities to install and run it on their own; smaller, regional carriers may rely on Wireless Services to host it. Some carriers may use a combination of both deployment types, or even work in a third-party solution, as Nextel does. "We have incorporated into our network a number of 'smart' filtering technologies that adapt to new spamming techniques," says Wilkerson. "Also, the FCC has instituted a 'do not spam' list of carrier domains [www.fcc.gov/cgb/policy/DomainNameDownload.html#N], on which our domains are included." He adds that the increasing volume in spam recently required Nextel to augment its filtering capacity to avoid latency, although he says Nextel proactively alerts its key customers in the event of any service latencies.

Roaming Messenger Inc. offers a solution that's especially valuable for public safety applications: a mobile messaging platform, which Lei calls a "breakthrough" technology that's easily integrated into existing computer aided dispatch (CAD), incident management, and other systems. "It's an opt-in, end-to-end closed system," he explains. "When a message comes in, you know it's your agency's CAD; there's no way for a stranger to spoof an e-mail, or worse, an emergency call."

Networked to virtually every device officers use, including mobile phones, PDAs, in-car laptops and desktops, Roaming Messenger gets critical information to officers in the field as quickly as a radio call; messages aren't buried underneath layers of spam e-mail or SMS messages.

First, the CAD system communicates with the Roaming Messenger Gateway to send an alert message. From there, the message literally "roams" from device to device — an officer's or detective's cell phone, desktop computer, laptop and PDA — until the recipient responds to its sounds, vibration or flashing light alert. Then, the interactive messenger asks for user authentication, usually a personal identification number.

From there, the messenger presents a number of interactive elements, including buttons and drop-down lists, which make decision making easier. For instance, supervisors can select a team leader for a specific incident. "It's a higher level of communication," says Lei. "An e-mail tells a recipient only passive information, such as location. Likewise, radio communications are limited because they rely only on voice. Roaming Messenger enhances existing means of communication by giving dispatchers and responders the ability to communicate visually, sending maps and photos along with text, without the worry of losing the message."

Roaming Messenger consists of a software engine placed on "smart" phones like those based on BlackBerry or Microsoft operating systems, with a server located in the facility. In this way, it completes the end-to-end closed network with its own messenger channels. The Roaming Messenger Engine listens not for incoming e-mail or SMS messages, but instead for the Roaming Messenger Gateway to notify it of a pending alert.

Equally important to the closed-network model is a way to secure it. Roaming Messenger includes 3DES encryption at the gateway level. Between the gateway and the originating device, the application uses Secure Socket Layer (SSL) security, and alert messages demand authentication before the recipient can view them. Lei says these security measures don't require much configuration, making security an out-of-the-box feature.

"Spam is a threat more than a nuisance, because the more it occurs, the more desensitized you become, and the less likely you are to respond to urgent messages in a timely manner," says Lei. "Users in mission-critical fields can't afford for that to happen."

Christa Miller (www.christammiller.com) is a freelance writer based in southern Maine.