My code is too long but basically the main program has this structure:
GLOBAL level%=1
//Load resorces:
LOADSOUND "Sound1.wav", 0, 2
LOADSOUND "Sound2.wav", 1, 2
LOADSOUND "Sound3.wav", 2, 2
LOADSOUND "Sound4.wav", 3, 2
LOADSOUND "Sound5.wav", 4, 2
WHILE TRUE
SELECT level%
CASE 1
GOSUB LEVEL1
CASE 2
GOSUB LEVEL2
ENDSELECT
PRINT "Push space bar",10,10,1
SHOWSCREEN
WEND
SUB LEVEL1
WHILE TRUE
// Do level 1 stuff
IF KEY(57) = 1
PLAYSOUND (0,1,1) //Here plays fine
PLAYSOUND (1,1,1) //Here plays fine
PLAYSOUND (2,1,1) //Here plays fine
PLAYSOUND (3,1,1) //Here plays fine
PLAYSOUND (4,1,1)//Here plays fine
level%=2
RETURN
ENDIF
WEND
PRINT "Push space bar to level 2",10,10,1
SHOWSCREEN
ENDSUB
SUB LEVEL2
LOADSOUND "newSound.wav", 4, 2
WHILE TRUE
// Do level 2 stuff
IF KEY(57) = 1
PLAYSOUND (0,1,1) //Doesn't play in iPhone. Yes in PC version
PLAYSOUND (1,1,1) //Doesn't play in iPhone. Yes in PC version
PLAYSOUND (2,1,1) //Doesn't play in iPhone. Yes in PC version
PLAYSOUND (3,1,1) //Doesn't play in iPhone. Yes in PC version
PLAYSOUND (4,1,1)//Here plays fine the new sound.
level%=2
RETURN
ENDIF
PRINT "Push space bar to level 1",10,10,1
SHOWSCREEN
WEND
ENDSUB