After you installed the applications on iPhone/iPod Touch, Apple can disable them remotely. This may be useful if there are any unstable or malicious apps. But, it has raised a serious privacy concern. If you don’t want the app to be removed suddenly, you can jailbreak the iPhone first, then install BossPrefs from Cydia. Choose “More” from BossPrefs. Click “Disable Apple App Killswitch”. You are now “safe” from Apple, at least in iPhone/iPod Touch firmware 2.0.1.