Not long ago I bought a Nokia C3-00. This is not a smartphone but it has wifi and a qwerty keyboard. I looked around and there were several J2ME apps that claimed it would allow to remote-control a PC but none was suitable or working properly for a media center like use. I decided to write my own, extremely basic, just enter the ip and port of the PC (Broadcaster plugin for EG) and the phone will just send the code for any key pressed as an UDP message, nothing more, nothing less.
The program catches the basic J2ME "actions" (directional keys etc), the non-standard qwerty keys (luckily enough the C3 sends the ascii code) and some basic commands added with XBMC in mind.
Anyway, this applies to a very thin layer of phones, good enough to have wifi, not good enough to use one of the decent "remote control" apps, but if you are right in that layer it may be of use
Well, that's it.
Bye