FWIW, I've sent pictures from Sony-Ericsson camera phones to my N800 without problems. I just select a picture on the phone and select send via BT, it finds the N800 while scanning (if set to visible), and there's a pop-up on the N800 where I can choose to ignore, save or save+show.
The devices don't have to be paired. In fact while sitting here in the office the N800 suddenly received a picture from someone on the floor below me.. must have selected the wrong destination. I don't know what kind of phone that was. Anyway there's still the pop-up so it's not like you're open to being spammed with stranger's pictures..