Border crossings

They're shaped like pizza boxes, and packed with processors and circuit boards. And their name, "session border controllers," conjures up images of sentries along the Rio Grande.

But these controllers have revolutionized the fast-growing business of sending voice signals and telephone calls over the Internet and, in the process, propelled Acme Packet Inc., a Burlington telecommunications company, to the top of the Globe 100 list of the best-performing initial public offerings in Massachusetts in 2006.

Start - ups like Vonage Holding Corp. and Skype Inc., as well as giants like Verizon Communications Inc., have begun routing telephone calls over the Internet rather than over traditional phone lines. The service -- known as VoIP, or voice over Internet protocol -- is much less expensive than traditional phone service, and offers customers options like taking their phone with them when they travel. While less than 10 percent of voice traffic now moves over the Internet, analysts say that share could grow to as high as 40 percent over the coming decade.

Acme Packet, a "playfully irreverent name" alluding to the old Road Runner cartoons, according to Andy Ory , its president and chief executive, is capitalizing on that growth. The company went public on October 12. As of March 30, its shares had climbed 55.6 percent, to $14.78. That was more than double the 22.8 percent appreciation of the second-largest gainer among last year's IPOs, Double-Take Software Inc. of Southborough.

The state's nine-member IPO class of 2006 was smaller than its immediate predecessor in 2005, when 15 companies completed stock offerings. But with IPO registration activity picking up momentum in the first quarter of 2007, last year's IPOs may be leading indicators of things to come. "It wasn't a huge class, but it was what we're hoping will be the be ginning of a new wave," says Maria Lewis Kussmaul , founding partner at Boston investment bank America's Growth Capital. Overall, the performance of last year's IPOs has been mixed. In addition to Acme and Double-Take, two other newly public companies have experienced double-digit stock growth. Shares of Metabolix Inc. of Cambridge increased 18.8 percent as of March 30, while shares of Oxford's IPG Photonics Corp. rose 18.4 percent.

The shares of others that went public in 2006 have been flat or down, with Boston's NewStar Financial Inc. slipping 1.4 percent by March 30 and Burlington's LeMaitre Vascular Inc. falling 8.9 percent.

Last year's most successful IPOs were companies like Acme Packet that positioned themselves at the front of an emerging business wave, waited until they were profitable, and had a strong roster of customers before taking the IPO plunge, Kussmaul notes.

Ory, a serial entrepreneur, recalled meeting his longtime colleague, Patrick MeLampy, at a Dunkin' Donuts in 2000, shortly after Ory sold his last company, and talking about the opportunities in new signaling systems for the Internet protocol networks that were springing up to carry voice and other data quickly and cheaply. They co founded Acme Packet to market session border controllers. The controllers route data between networks, enabling Verizon customers to talk securely with customers of AT&T Inc., for example, via the Internet.

In 2005, as networking giant Cisco Systems Inc. was readying a competing product, MeLampy, now the Acme chief technology officer, "ran into my office and said this is the time to go public," Ory says. "Going public has let customers feel more comfortable with us and feel they can make longer commitments."

The company today has about 300 employees, and more than 360 customers in about 75 countries. Its biggest customers include Sprint Nextel Corp., Siemens AG, Alcatel-Lucent, and Time Warner Cable Inc. Joe McGarvey , senior analyst at Heavy Reading, a technology research firm in New York, says Acme Packet has distanced itself from competitors . "They're completely focused on their technology," McGarvey says.

Robert Weisman can be reached at weisman@globe.com.