I recently purchased a Sony Ericsson w610i set. If you know me, despite being related to IT, I am not a mobile phone/ gadget freak. This is the first set that I have bought (earlier ones were gifted). A good review of the set can be found here.
Many features of the phone remind me of the early days of personal computers -- of the difference between the electronic circuits and the interpretation of the electrons running through them.
Hardware manufacturers come up with a very well-thought product range; each variation is given a meaningful model number. For example, the "w" in w610i probably stands for "walkman", indicating the dominating music features of the phone. (By the way, do you know "walkman" is Sony's trademark? Walkman's history tells you that the initial attempts to market the product met with little success.) Whenever you see a hardware model, be assured that there is a rationale behind the model numbering. See, for example, how Intel numbers its processors.
Comparatively, I feel ashamed how vague is software versioning and packaging. On the brighter side, software continues to push hardware to its limits. Just like early days of PC, amateurs continue to write software for PDAs and mobile devices. They hack stuff to provide you with more than what comes out of the box. Two very nice examples for Sony Ericsson sets are Float Mobile Agent (Fma) and My Phone Explorer (see the screenshots below). Fma is open source and My Phone Explorer is freeware.
These software let you do amazing stuff like taking complete control of your phone from your PC; take backup of everything in your phone and later restore it; etc. MyPhoneExplorer additionally lets you install .jars into your mobile phone.
Coming to the software side of the Sony Ericsson mobile set, it runs Symbian as its operating system, and of course Java ME. Sony Ericsson has a very nice Developer's Forum for their products.