Paring a Sony Ericson T610 cell phone with a Mac via Bluetooth. This phone was so heavily promoted last holiday season that I got sick of it before I was even interested in getting a new phone. But my current phone is pretty battered, and those Bluetooth headsets are pretty sexy. Recently reported security issues supposedly have been fixed in newer phones, and older phones can get an upgrade.
It's especially nice to have confirmation that some of these newer cell phones support direct uploading of MIDI files for ringtones, images, and even J2ME software. When the first polyphonic ringtone-supporting phones came out, I had wondered if they used proprietary formats that required that everyone pay someone, such as the cell service provider, for the privilege of using a custom ringtone. It was surprisingly difficult to confirm or deny this with casual web searches: search engines are pretty clogged on the subject of cell phones, with a million web sites wanting to sell you ringtones for $3 a piece or give you lousy free ringtones so they can display more ads, and a dozen other sites dedicated to clogging search engines, with phrases like "free ringtones" repeated a thousand times on a page. In many cases, not even product manuals say anything about support for uploading MIDI files as ringtones. So it's nice to have confirmation that these phones indeed provide such support.
Sony Ericsson's developer site pretty much answers my second question, how easy is it to write my own software for a phone that ostensibly supports J2ME. Their SDK and emulator are written for Windows, but there might be ways around that. The T610 supports on-device debugging (though it's obviously not a substitute for development with an emulator).
Club Sony Ericsson has some good information and resources.
