Fieldrunners took off in popularity on the PSP as it quickly gained word-of-mouth buzz that it was one of the better tower defense games. That popularity provided the incentive for Subatomic Studios to port the game to the PSP and now to the DS.
Available for download from the DSiware service, fieldrunners is available now for 500 points ($5.00).
Fieldrunners has the player fighting off waves of attackers by setting up a variety of towers that will fire at the attackers. Each attacker killed gains the player money allowing the towers to be upgraded to fight off even more powerful attackers.
The fact that DSi is getting iPhone ports should be as clear an indication as any of how sweeping a success the iPhone has been.