The xmms2_blue client interfaces xmms2d to a Bluetooth enabled phone. It is still fairly experimental, but basic functionality should work. The protocol used is described in Ericsson and Sony Ericsson documents. So most likely the client will only work with phones of those brands. The sources can be obtained form the blue branch of Jens Taprogge's xmms2 git tree at https://github.com/XMMS2/xmms2-alumni/.