Perhaps this is the most widely asked/answered question everywhere.. i couldnt figure out this one thing.. To enable multitasking, We HAVE TO SET THE BASE SDK 4.0 in project settings. that does the job alright... but after that, does it remain compatible with 3.x?.. its only those 4 methods in appdelegate that were added... will they be ignored in 3.x? and whats the way to test it???