Some definitions

mySTEP http://www.quantum-step.com/wiki.php?page=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) 4.x
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 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 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 (difficult to estimate) ca. 10 Mio
Backed by FSF GNUstep project, quantum-step.com Apple