It is our intention to support every feature of every phone. Note that there is absolutely no documentation for most of the phones out there. The developers have to sit there and work it all out, which can take a considerable amount of time. In many cases the phone vendor only ever intended for the phonebook to be accessed and nothing else, so we have to work out techniques to reliably access the other features. Most of the phones also have various bugs and quirks we have to identify and work around.
The features and phones supported depend on access to the phones, developer priorities and time available. There is no formal plan, so the answer is "whenever a developer gets round to it, and has access to a phone".
In general if we don't have access to the phone, it will take a long time. You can see the list of phones supported and what the developers have on the phones page. You can speed things up by loaning a phone to the developers (buy them on eBay). Details.
BitPim Online Help built 17 January 2010