Having Synology diskstation, notebook with XBMC and smart phone with Symbian, it should be possible to make all these talk together being able to play music stored on the diskstation using XBMC and controlled by phone, right?
I tried to set it up some time ago, but I used samba export on the diskstatio and all I found for controlling was XBMC Symbian S60 Remote v2, which is indeed useful, but choosing what to play remotely is quite limited. Luckily yesterday I've discovered world of DLNA aka uPNP and was surprised that this works pretty well. I've configured diskstation to behave as a uPHP media server, XBMC is able to act as media renderer and my Nokia E52 has ability to act as a controller. If you are lost in these terms, good overview is available here.
Well the control interface of Nokia E52 is far from perfect, but still provides good way to control all the stuff. Maybe I will look for some other solution in future, I'm sure it will exist as well.