Hay I just have one question, In the first lvl of Mercanaries 2

You have to press up on the pad not the joystick

The air strike your referring to is an air strike with a satellite. Most of the air strikes you will get from the guerrillas or the other beggining groups will only have smoke signals. There are a few that use other signals but most are smoke signals. If you really get on the good side of one of the begining groups you may be able to get a satelite signal air strike. I don't think you can get a satellite guided air strike until you make relations with the UN or China. Good luck, its an amazing game.

P.S. Don't use cheat codes, the game is so much better with out them.

Later in the game you can buy more air strikes, or you can use cheats. To enable cheats, press Back to activate your PDA, then press LB, RB(2), LB, RB, LB(2), RB(3), LB. Then press Back. A message will confirm correct code entry. Then, enter this code at the PDA screen while the PMC on the map is highlighted to activate the cheat.
Right, Left, Down, Up, Right, Left, Down. This will unlock all the airstrikes except the nuke. To unlock the nuke as well, enter Up, Up, Down, Down, Left, Right, Left, Right.