Some definitions

[mySTEP] is the GNUstep based GUI toolkit (i.e. frameworks) extended by QuantumSTEP (which adds an application suite e.g. for address book, calendar, mail, etc.) to develop applications for Linux/X11 based handheld devices (i.e. Sharp Zaurus, OpenMoko Phone)
iPhone SDK is the Apple SDK to develop native applications for the iPhone and the iPod Touch

Comparison

	QuantumSTEP	iPhone SDK
Available for Developers	continuous progress since 2003 (mySTEP)	beta now, final June 2008
Frameworks	Foundation, AppKit, Small WebKit, PDFKit, IOBluetooth, X11Render, SQLite	Foundation, UIKit, WebKit, Core Audio, OpenAL, Core Animation, OpenGL, SQLite
SDK cost	free (cross-gcc, etc.)	free (by registration only)
Simulator	not required (100% same source code)	included
Development Systems	Mac: Xcode 2.4 or later, Interface Builder, Xtoolchain  Linux: Project Center, GORM coming	Intel Mac: Xcode 3.1, (Interface Builder coming), Linux: no
Minimum gcc	2.95.3 (with Obj-C 1.0)
Distribution of your App	free and open as you like and need	only through „App Store“ at 99$-299$/year + revenue sharing
Developer Program	none, but www.gnustep.org	appears to be initially limited and US only
Availability	since 2003 (mySTEP for Zaurus)	Beta: now, finally June 2008
Devices	Sharp Zaurus, OpenMoko, Acer n30, more to come	iPhone, iPod Touch, (more to expect, e.g. Tablet?)
GUI-Design	Interface Builder	by Code (IB coming)
License	LGPL	NDA
Restrictions	none imposed by project	type of applications is restricted (i.e. no download of other executables)
Installed Base (E2008)	10k ... 1 Mio	ca. 10 Mio
Backed by	FSF GNUstep project, quantum-step.com	Apple