In the world of video games, Rockstar Games’ upcoming April 28 release of “Grand Theft Auto IV: Liberty City” is generating as much buzz as the next Batman movie. And electronic game retailer GameStop has capitalized on that interest with a pre-launch GTA4 promotional game that integrated online, mobile and in-store activities.

From late March until Tuesday April 15, GTA fans could go to www.GameStop.com/GTAIV, and get a question related to the new game and a set of five multiple-choice answers. They could then text one of those answers to a mobile short code. Players who chose the right answer were then entered into a drawing for four chances to travel to the real “Liberty City”, a/k/a New York, for the game’s official unveiling and for a chance at one of 38 cash prizes stashed in a lockbox, including a $10,000 grand prize.

Fans were also able to enter the contest via the GameStop Web site, but incorporating mobile as a promotional channel was a no-brainer in the design of the sweepstakes, according to GameStop.

“Text-messaging has become a quintessential part of the lifestyle of gamers today,” said Joseph Heilner, director of marketing for the 5,200-store retailer. “It’s just a very natural channel for us to pursue to reach gamers in their natural environment. We’ve dabbled in mobile on a small scale in the past, but this is definitely the largest text component we’ve ever built into a game. And we anticipate that we’ll continue to build on this experience in the future.”

Heilner said the game was advertised with full-size ads on several popular game-related Web sites. The ads contained instructions for texting entries into the competition and direct visitors to the microsite for fuller instructions.

The prize portion of the game is built around a strongbox supposedly hidden in Liberty City by one of the game’s characters. Each of the four text contest winners will be given a key that opens that strongbox and the chance to take out one of 38 envelopes within. One of those envelopes holds a $10,000 first prize; another has a $5,000 second prize. There are also 10 $1,000 envelopes, six with $500 awards and 20 holding $100 each.

Those other envelopes will go to players who have discovered one of 1,000 sets of red keys that GameStop dropped in selected stores around New York between April 1 and April 27. Those keys were unmarked except for a 1-800 phone number. Players who called that number heard a recording instructing them to show up at GameStop’s NY flagship store at Broadway and W. 33rd St. on GTA 4’s April 28 launch day.

Once assembled, those NY regional players were randomly assigned an order in which to try their keys in the lockbox. Those with keys that successfully open the box got to remove an envelope, with play continuing until all the envelopes have been given out.

The key drops weren’t advertised or alerted either with online ads or in-store signs. “There’s really a coolness factor there,” Heilner said. “GTA 4 is a very edgy, hard-core game, and this target audience will really appreciate that kind of sub-cultural connection. Finding a key, calling an unknown number, getting a message from someone with a strong New Jersey accent: We wanted it to feel a lot less gimmicky and commercial than other game promotions out there.”

Heilner said in the first two days after the competition launched on March 24—and with online ads placed in only the first of several Web gaming sites—GameStop already notched 4,500 registrants.

“This promotion is getting to the hard-core gamer in a way that they want to be reached,” he said.

Players had to be at least 18 years old to take part in the game, corresponding to the age restriction on the “Grand Theft Auto: Liberty City” game itself.