There are now more apps than ever for the iPhone. (Photo by Ricky Romero via Flickr)

As Columbia University graduate student Christian Roman sat among friends at a bar one evening, he asked Samuel L. Jackson a sports question that had been on the minds of a lot of New Yorkers lately.

“Will the Knicks get Lebron James?”

“Not just no,” Jackson shouted back, “HELL, NO!”

The world famous actor wasn’t actually there, of course. Roman was using the new ISamJackson app for his iPhone. Now the star of “Pulp Fiction” and “Snakes on a Plane” is Roman’s constant companion, dispensing advice and offering random words of wisdom at the touch of a button.

“I like having Samuel L. Jackson’s advice at my fingertips,” Roman said. “He has such a distinctive voice and I love hearing it say these crazy things whenever I want.”

ISamJackson is one in a slew of celebrity iPhone applications flooding the marketplace that connect people with their favorite stars via their phones. Lady Gaga’s app lets you sing along to her hit singles, while the apps for MC Hammer , Keanu Reeves and Snoop Dogg provide constant news updates on those stars. Jessica Simpson’s offers some famous quotes by the singer.

All of these celebrities, and plenty more, are trying to muscle in on the market for iPhone apps, a $4.2 billion industry last year, according to Gartner, a business technology research firm. They are crowding the already packed market for iApps, which numbers some 100,000, and sales of apps of all kinds are expected to reach over $6 billion in 2010, according to Apple.

Some of the best apps, according to Brad Spirrison, a technology writer for the iPhone technology Web site Appolicious, are from talk show host Ellen DeGeneres, the musical group Black Eyed Peas and singer Mariah Carey.

With Carey’s app, called Mariah Carey-oke, the iPhone uses voice recognition technology with special headphones so users can sing along to Carey’s songs and score themselves on their karaoke skills . The more lyrics they sing correctly, the higher the score. Of course, the songs are from Carey’s  most recent album, so Carey fans who want to hear her ’90s are out of luck.

The “Ellen Show” app offers news, videos, photos, and even games from the show. One feature lets you guess the comedian by watching a segment with DeGeneres and a comedian whose face is blocked so users can guess his or her identity.

With the Black Eyed Peas’ app, fans can play video games set to the group’s music with themes taken from their most popular music videos like “Meet Me Halfway.”

According to app producers, Apple takes 30 percent of all profits on apps, while the software developer and celebrity split the rest. Some celebrities, like Jackson, receive an up-front fee. But more often than not, the motivation is to promote their brand through new media.

Many of the celebrities with iApps are not what one would call A-list, however. Reality show couple Heidi Montag and Spencer Pratt, never ones to miss out on any avenue of self-promotion, recently released an app called SpeidiWeb. For $1.99, fans get unlimited access to news photos, and videos of the couple, as well as music from Montag’s newest endeavor: a pop album appropriately called “Superficial.”

And fresh off his stint on the widely-mocked MTV reality hit show “Jersey Shore,” DJ Pauly Delvecchio (better known as merely Pauly D) released an app earlier this year that features more pictures of himself shirtless than of his music mixes.

Just like celebrities themselves, some of the apps are D-list, according to Spirrison. “Though some apps have a low replay value and don’t offer a lot of technical ah-ha moments, they’re still fun to play with and show off to your friends,” he said, referring to apps like Pauly D’s and Reeves’. That’s because they use virtually the same template and provide only bare-bones links to a celebrity’s photos, Twitter feed and news updates, but no interactive features.

Then there are the oddball apps, such as one produced by the firm Rock Software, for Cincinnati Bengals wide receiver Chad Ochocinco. (He used to be Chad Johnson until he changed his last name two years ago so it is now his jersey number in Spanish.)

For $2.99, serious fans can download The Chad OchoCinco Experience complete with his favorite songs and a Where’s Ocho? feature that uses GPS to track and map the athlete’s location at all times. On Feb. 23, for example, the app reported that Ochocinco was in southern Florida.

Fans can also receive “Tips From Ocho,” with such aphorisms as “Haters are confused admirers, they can’t be or figure you out so negativity comes out their mouth.”

The most popular celebrity app is I Am T-Pain, averaging  10,000 downloads per day according to Apple, and ranked 35^th overall.  It belongs to chart topping rapper T-Pain (Faheem Najm) who uses Auto-Tune technology in his songs. His app allows fans to do the same with its karaoke feature. First, users sing along to a T-Pain track such as “Bartender” and “Buy You a Drink” using the small microphone in most iPhone headphones. Then, the app plays the song back to you, but morphs your voice recording by using T-Pain’s signature Auto-Tune technology.

One app that hasn’t quite reached the prominence of T-Pain’s is Ask the Hoff, David Hasselhoff’s newest contribution to iPhone users that allows fans to ask him yes or no questions in a magic eight ball style format. His answers are touted by his company, HotStuff Productions, which produced the app, as “Hoffalicious” advice, even though he’s just giving yes or no answers to questions.

As for ISamJackson, just 99 cents provides access to over 150 original sound bites, including a feature where Jackson’s unmistakable voice answers questions. The software company HeatWave created Jackson’s app, which is also listed as a top seller on Apple’s iTunes store. It’s the app’s interactive qualities that make it so popular, according to producer Tim Schubert.

“The coolest part about iSamJackson is its ability to inject him into a conversation,” Schubert said. “There are a lot of things that can’t be said by the regular Joe, but if you have iSamJackson in your pocket you can get away with anything. Playing even the most ruthless quotes in the app results in comic relief, which can be great for a meeting that’s gotten unruly or satisfy the occasional need to mock a friend.”

Or, as Roman discovered on a recent Wednesday evening after class, even culinary advice: “Should I have McDonald’s for dinner?” he asked the app.

“Are you out of your mind?” Jackson’s voiced thundered back.