You can use PyObjC on the iPhone as well, due to the excellent work by Jay Freeman (saurik). See iPhone Applications in Python.

Note that this requires a jailbroken iPhone at the moment.

Not currently, currently the only languages available to access the iPhone SDK are C/C++, Objective C and Swift.

There is no technical reason why this could not change in the future but I wouldn't hold your breath for this happening in the short term.

That said, Objective-C and Swift really are not too scary...

2016 edit

Javascript with NativeScript framework is available to use now.

Yes you can. You write your code in tinypy (which is restricted Python), then use tinypy to convert it to C++, and finally compile this with XCode into a native iPhone app. Phil Hassey has published a game called Elephants! using this approach. Here are more details,

http://www.philhassey.com/blog/2009/12/23/elephants-is-free-on-the-app-store/

The iPhone SDK agreement is also rather vague about whether you're even allowed to run scripting languages (outside of a WebView's Javascript). My reading is that it is OK - as long as none of the scripts you execute are downloaded from the network (so pre-installed and user-edited scripts seem to be OK).

IANAL etc etc.

BeeWare is an open source framework for authoring native iOS & Android apps.

2019 Update:

While Python-iOS development is relatively immature and likely will prevent (afaik) your app from having native UI and functionality that could be achieved in an Apple-supported development language, Apple now seems to allow embedding Python interpreters in Native Swift/Obj-C apps.

This supports importing Python libraries and running Python scripts (even with supplied command-line arguments) directly from your Native Swift/Obj-C code.

My company is actually wrapping our infrastructure (originally written in Python) in a native iOS application! It works very well and communication between the parts can be easily achieved via a client-server model.

Here is a nice library by Beeware with a cookiecutter template if you want to try and run Python scripts in your iOS app: https://github.com/beeware/Python-Apple-support/tree/3.6.

You can do this with PyObjC, with a jailbroken phone of course. But if you want to get it into the App Store, they will not allow it because it "interprets code." However, you may be able to use Shed Skin, although I'm not aware of anyone doing this. I can't think of any good reason to do this though, as you lose dynamic typing, and might as well use ObjC.

The only significant "external" language for iPhone development that I'm aware of with semi-significant support in terms of frameworks and compatibility is MonoTouch, a C#/.NET environment for developing on the iPhone.