I suggest you look into the messaging protocol used by samsung and any other apps.

If you can provide these people may be more interested in looking into implementing them.

To be honest the greatest use I can think of for such an app is teenage girls passing free messages in class.

But I have been in a few meetings that would make this useful (because free) but it would rely on using a standard that could be implemented on most bluetooth phones.

hence look into the protocols used and see if we can copy them Having the n900 able to mimic multiple other phones would be poss?

http://en.wikipedia.org/wiki/Bluechat