I don't build apps, but I have done mobile websites. I hand code them in Notepad+ because I enjoy that kind of thing but if you don't, try Mobify and Onbile if they're still around. With how good phones and tablets are at displaying my site these days, I ditched a mobile version long ago. It was nice before touch screens, as you can shortcut links to numbers, but mostly useless now. I coded in WML, but have moved onto XHTML-MP like everyone else
Things to remember about a mobile site:
-Minimalism. Most people who use mobile sites are using old phones (or even slow computers). The more gratuitous content there is, the less likely they're going to be happy
-Know your audience. Unless your full site is very graphics intensive, has flash, or something else that annoys iPhone users, it's mostly going to be those not great with technology. If your full site is one of those things, just make sure you give smartphone users a bit of eye candy
-Test. A lot. From every phone, pc, and tablet you have access to.
-Keep it as current as your non mobile site.
