Starting with iOS4 developers have access to a set of APIs. Audio, GPS + 'Location', Push, Phone (think Skype), Worker and probably a few other APIs. Until now

Starting with iOS4 developers have access to a set of APIs. Audio, GPS + 'Location', Push, Phone (think Skype), Worker and probably a few other APIs. Until now, when the user pressed the home button you were able to write your state to flash if necessary. Now there is another way to 'freeze' your app and keep the state in memory -- at least until iOS4 decides your app won't be needed soon and fully quits it to free memory. If you use the APIs mentioned above it is possible to continue playing (streaming) music, doing something else during a Skype call or update your location whenever you connect to a new cell tower* . If you need turn-by-turn you get access to constantly ask for GPS, this aside from calling/playing music is the only 'real' multitasking as it continues in the background until you tell it to quit. The Worker API allows you to complete a task, for example continue uploading that video file to Dropbox. Once it's done the Dropbox app quits (or is frozen in memory as everything else). Push notifications allow to access a server but it seems as someone else here mentioned the payload is too low, and only accessible as soon as the app is activated. I can't tell for sure though as I'm not an iPhone developer just following it closely and most of this information comes from the January(?) keynote when iOS4 was introduced. *Because GPS sucks battery you app gets called whenever you connect to a new cell tower, this according to Apple, should be sufficient for services like Google Latitude where the exact position at any given point isn't that important like it is for turn by turn navigation.