I'm trying to get a grasp of what the software mobile world is made of. What are the operating systems or application layers used by Mobile devices nowadays? Not only PDAs/SmartPhones, bu also regular phones.
One trend I see are that Adobe focus harder than ever on the mobile platform. The hardware on the phones are now at the point that you can use the same Flash player on the phone as on your computer, not a Flash Light version.
On the Adobe Max in San Francisco 08 they showed examples on that (running Flash Player 10 on the phone) for HTC, Samsung, Nokia, Google(Android) (and soon on the iPhone they say). That will open up for a lot of developers to attack that area which has been kind of a kinky work with all the bugs and different hacks for different models, unsupported workarounds and so on.
With the new tool that creates installation packages for the different platforms (windows mobile, symbian and other) it will be a little bit easier to deploy also.
Iwould care less for "trends" if I were you and just try to keep close to standards like (X)HTML and get "everything for free" anyway... ;)
"Regular phones" use Java (J2ME, MIDP2.0 if you're lucky), or HTML in the browser (the browsers are getting better). WAP still exists and is supported, but is best avoided, IMO.
There are other environments like Flex, Silverlight which may become more prevelant, but right now they're simply not on most of the phones people have, and can't be added later.
Smartphones (to me, the definition of a smart phone is one that runs additional applications beyond the J2ME type) still run a variety of things.
There's also an increasing tendency to use the browser (especially as increasingly powerful ones come with the phone or can be installed - e..g Opera).
Native applications are still a disparate variety. Symbian (Nokia, largely) is C++ natively, but Python and others exist (pretty niche environments, though). Windows Mobile is either C++ or .NET (mostly C#, in my experience). Blackberry is J2ME, although rather more capable than for featurephones.
There are some attempts to implement .Net on Symbian (e.g. http://www.redfivelabs.com/) but I'm not seeing these get much traction.
Summary: it's still a mess. If you can, pick a platform and stick with it. If you need to run on everything, good luck, you're going to need it