As a .Net developer I always dreamed for the possibility to develop with my existing skills (c#) applications for the Iphone.
Both programs require a Mac and the Iph
I kinda like the idea of providing means to quickly get a grip on iPhone dev with techno people already know. I personnaly, as a Java developer, use iSPectrum (http://www.flexycore.com). It also come with an IDE, debugger and stuff, which make it really convenient to develop with because it benefits of all the power of Eclipse Java plugin. Being based on Java, this also allows to easily reuse already existing code from other java apps, which can be really handy providing that Java is present on almost all platforms (desktop & mobile alike) except iPhone. Plus it's free for open source projects.
I'd rather consider these kind of solutions, because I don't like the idea of coming back to developing in emacs :) .