Hudson Soft announced the release of AR Monster, an iPhone (3GS only) roleplaying game integrating augmented reality technology, which it has made available for free for the next two weeks as part of a grand opening sale -- so make sure to pick it up before July 4th.

In AR Monster, you use your iPhone's GPS system and camera to discover and battle more than 600 monsters hidden in the real world. By playing the game in different locations and pointing the handset in different directions, you'll be able to find new kinds of monsters.

Once you've found a monster, you can attack it with up to six different kinds of weapons, each taking advantage of different weaknesses a particular monster might have. Once you've defeated a monster, it's registered in your "Book Of Sealing". As with Pokemon, the goal is to catch register them all!

AR Monster uses OpenFeint to offer global leaderboards, achievements, and other features that take advantage of the mobile social network. Hudson says it also plans to release a future update that will add monsters from Aurora Feint 3 (developed by the makers of OpenFeint).

"With its innovative augmented reality technology, AR Monster is a great addition to our iPhone game portfolio," says Hudson Soft's Smartphone Business Division president Masato Shibata. "We think that we’ve created a fantastic role-playing game for our players, with over 600 fierce monsters to battle and 6 awesome battle weapons to choose from."