According to IGN, the easiest way to get a helicopter in "Grand Theft Auto: Liberty City Stories" is to use the in-game cellphone and dial 359-555-0100. When calling this number while outside, the player gains access to the Annihilator helicopter.
Helicopters are not the only vehicles players are able to spawn automatically using the in-game cellphone. Other vehicles attainable in this way include the Jetmax boat by dialing 938-555-0100, the NRG-900 motorcycle by dialing 625-555-0100 and the Super GT car by calling 227-555-0168. The phone is also used to summon other items and in-game perks, such as weapons, infinite health and the ability to reach secret locations.