Found this useful comparison of mobile development platforms on Wikipedia. It covers the main ones such as J2ME, BREW, Symbian, PalmOS etc. but also the (relatively) new kids on the block such as Android and iPhone.
As well as the comparing the capabilities and strengths of each platform; it also compares their existing deployment patterns and technology dependencies e.g. although BREW is now also supported on GSM/GPRS networks; its penetration has been minimal and it is still used predominantly by CDMA carriers in the US and South Korea.