Wireless carriers will have to fortify their defenses in the battle against text-messaging spam or eventually risk a customer revolt, industry watchers say.

But if they clamp down too hard, too soon they might face a different risk: losing revenue. Some experts say this conundrum accounts at least in part for the less-than-vigorous countermeasures deployed to date.

Because wireless spam is still in its infancy in this country, carriers are just beginning to respond to the problem with filters and policies, although these tactics aren't necessarily designed to fight spam in the form of text messages. Critics argue these attempts to protect subscribers from spam aren't enough and belie a greater concern for the bottom line than protecting customers.

"The more text messages received and sent by a subscriber, the more money the operator makes," says Bob Egan, CEO of consulting firm Mobile Competency. "It's a business conflict; if I stop this I'm going to lose revenue." The carriers are doing just enough spam filtering to prevent unwanted messages from overwhelming subscribers but not enough to keep themselves from making money, he says.

One carrier dismisses this theory. "A call to our care center is much more expensive than [the revenue generated by a] text message; we really see this as a customer satisfaction issue," says Bob Ewald, senior director of core data services at Nextel.

"As time goes on and the anti-spam filters become more effective, less spam will get through," Ewald says. The number of unwanted text messages crossing Nextel's network has increased over the past year, accounting for 45% to 60% of all Short Message Service (SMS) messages, he says. About a year ago Nextel began using anti-spam filters and white and black lists, resulting in a significant drop in complaints from subscribers.

None of the carriers interviewed would break out revenue figures for text-messaging services, but Verizon Wireless says its data services in general represent the fastest-growing portion of its business from a revenue perspective.

"Any business is not going to interrupt its profit stream unless they are forced to," says Frank Gillman, director of technology at Allen Matkins law firm in Los Angeles, which has 250 Verizon Wireless subscribers. "It's all driven by customer demand, and right now people aren't complaining about wireless spam."