The current iPhone still has a nasty limitation. 3rd party iPhone applications can not run in the background and must shutdown after closing.
Last year Apple said it would support a push notification service so apps that need updating from server side information can do so even if they are not running.
The push notification service got delayed and now a rumor on MacRumors points to Apple actually enhancing the iPhone firmware to allow background processes. This would definitely be the cleaner solution and would position the iPhone OS to better compete with the other smartphone OSes in the market that support background processes.
Background processes for the iPhone might be coming in the iPhone 3.0 firmware release that could already come this June with a new iPhone handset release. The new iPhone 2009 is rumored to have more CPU power and background processes would be no issue on that device.