AT&T on Monday signaled its entry into the mobile enterprise market with hosted and managed services that allow companies  to extend their business applications out to mobile devices.

The No. 1 U.S. carrier joins a pack of companies already in the market, including handset makers Nokia, RIM, and Apple, along with Microsoft and IBM, and a number of small companies such as Antenna Software.

Jersey City, New Jersey-based Antenna Software develops and markets the middleware that AT&T will use to deliver its new mobile enterprise services.

Until recently, the mobile enterprise was relegated to very slow email. But the emergence of smartphones, 3G networks,smarter application design, and cloud computing have made true mobile enterprise computing a possibility.

“We think the industry is seeing the perfect storm that makes mobile applications a reality,” said Eb Keshavarz, AT&T’s vice presidentof business development. “The application market outside the mobile space is more than $30 billion but the amount spent on mobile is tiny.”

Now AT&T, which made its first major foray into wired application hosting six weeks ago, is venturing further with the announcement of its mobile application hosting service. (see AT&T Floats into  Cloud Computing)

AT&T, which will focus its efforts on nine different markets including financial services, construction, and healthcare, will use the combined capacity of its 38 data centers to drive both its wired and hosted mobile services.

The service is currently available on 25 devices including the BlackBerry Pearl, BlackBerry Curve, Motorola Q9, Palm Centro, Palm 750, and Blackjack.

AT&T is a customer of its hosting partner Antennae Software, which after 10 years in business finds itself at the center of a market that is suddenly coming of age.