iOS Background App Kludge
iOS 4 includes seven multitasking services, but none of them are conducive to running a utility service in the background. An application can run in the background to get updates from the GPS, but Apple won’t allow it to run in the background to get updates from IM, Twitter, or a mail server. (Apple’s own Mail app is exempt from this rule, of course.)
The developers of Pastebot wanted to run their app in the background to listen for updates from their companion Mac utility. Their solution is to use the multitasking service that lets apps play music in the background (via John Gruber). They thoughtfully included a silent audio clip so that this kludge would be invisible to the user and not drain the battery. Apple rejected the app, saying that the music must be audible.
So, instead, you must create or buy a silent audio clip, put it in iTunes, sync it to your iPhone, and select it in Pastebot’s settings, all to work around Apple’s decision to forbid normal background processing. This makes the app more difficult to use and wastes the time of both the developers and the users.