Is there such a thing? Mac OS X was based on BSD Unix so is it possible? Or from what I have heard, there is a MonoDevelop plugin that has an iPhone sim.
OSX is based on BSD, not Linux. You cannot run Xcode on a Linux machine.
Nope, you've heard of MonoTouch which is a .NET/mono environment for iPhone development. But you still need a Mac and the official iPhone SDK. And the emulator is the official apple one, this acts as a separate IDE and allows you to not have to code in Objective C, rather you code in c#
It's an interesting project to say the least....
EDIT: apparently, you can distribute on the app store now, early on that was a no go....
The low-level toolchain for Xcode (the gcc compiler family, the gdb debugger, etc.) is all open source and common to Unix and Linux platforms. But the IDE--the editor, project management, indexing, navigation, build system, graphical debugger, visual data modeling, SCM system, refactoring, project snapshots, etc.--is a Mac OS X Cocoa application, and is not portable.
If you run VMware Player or Workstation (or maybe VirtualBox, I'm not sure if it supports Mac OS X, but may), and then Mac OS X Server (Client can't legally be virtualized). Of course, in this case you are running XCode on OS X, but your host machine could be linux.