I thought it would be nice to have some sort of a summary about the different languages which can be used to program mobile phones. I also thought I would be able to come up with a good list in few minutes, but after spending some time trying to come up with a great summary, I realized I need to settle with this half-baked version and hope I can update the list based on comments from you guys... (Thanks Paul for your comments!)

Symbian C++
Market: 100+ million Symbian devices, including S60 from Nokia
Pros: No execution overhead, best access to native capabilities (access to some capabilities requires Symbian signing) before any other development language, free SDKs and tools (to start with), localization framework
Cons: Steep learning curve

Java ME (MIDP2.0/CLDC1.1)
Market: 1+ billion devices (including MIDP 1.0 devices), almost all new phones are Java ME enabled
Pros: Largest market, free tools (a choice of) and SDKs
Cons: Fragmentation (support of APIs, screen sizes, memory, etc.) causes a lot of work in porting, some native access lacking (and no JNI)

Python
Market: Not preinstalled on any devices, on S60 phones only
Pros: Open Source (source available), easy to get started, extensibility (getting better access to native capabilities all the time), excellen prototyping tool
Cons: Work in progress, very limited market - requires users to install Python environment on their phones (although it is possible to create stand-alone Python apps), pain to debug features not supported by the emulator

Flash Lite
Market: 100+ million, preinstalled on newer S60 and Series 40 devices, available for download
Pros: Programming for non-programmers, same great tool as with Flash for desktops, not much fragmentation, very good and upgradeable emulators, player scales the UI (vector graphics)
Cons: Flash Authoring tools is expensive (30-day free trial is available), Flash 1.1 (most of the devices on the market) is very limited in capabilities (for example not Bluetooth support), integration with browsers not available on many devices

A couple of unfinished tools to follow...

Ruby
Market:
Pros:
Cons:

Browser
ECMAScript (Series 40), JavaScript (S60)
Pro:
Cons: