First, let me say I'm not against jailbreaking nor am I arguing if jailbreaking is right or wrong. But I saw a thread about this topic and it got me wondering. So I went to read apple's EULA, the section about permitted uses and restrictions and here's what it says: You may not and you agree not to, or to enable others to, copy (except as expressly permitted by this License), decompile, reverse engineer, disassemble, attempt to derive the source code of, decrypt, modify, or create derivative works of the iPhone Software or any services provided by the iPhone Software, or any part thereof (except as and only to the extent any foregoing restriction is prohibited by applicable law or to the extent as may be permitted by licensing terms governing use of open-sourced components included with the iPhone Software). Any attempt to do so is a violation of the rights of Apple and its licensors of the iPhone Software. If you breach this restriction, you may be subject to prosecution and damages. So is it or is it not illegal?