If we accept a definition of killer app as a usage scenario (or a set of usage scenarios) that is very likely to result in the initial success of its associated technology, then what is the killer app for Bluetooth wireless communications? I submit that although the more futuristic and "cool" applications (such as those already cited) are interesting and potentially of significant value to users, the "killer app" for Bluetooth technology may be found in the simpler cable-replacement arena.
Specifically, the Bluetooth Special Interest Group (SIG) has put great effort into stressing interoperability of devices from multiple manufacturers; this is a primary purpose of developing and publishing the Bluetooth Profiles. Most suppliers of Bluetooth technology are interested in interoperability and ease of use of that technology (events called unplugfests, where vendors can informally test their solutions with each other, have been popular and successful). I believe that the initial success of Bluetooth technology is more likely to be fostered by excellent end-user experiences with the first products on the market. Because many users perceive value in being free from the hassle of cables, the ability to perform tasks such as dial-up networking, file and object transfer, synchronization, and voice communication wirelessly will help to prove the benefits of Bluetooth wireless communication.
Thus, it is my opinion that the "killer app" in this domain is really the collective usefulness, especially in terms of interoperability and ease of use, of early Bluetooth cable-replacement solutions. Indeed, if these initial products are to be widely accepted and achieve their full potential, they need to work well together, regardless of who manufactures the products. Users will rightly expect products with a Bluetooth logo to work well and to work without hassle. If this is achieved, I believe that a solid foundation will be laid for the initial and continued success of the technology. In fact, if the initial basic solutions were unsatisfactory and the technology did not live up to its potential, the opportunity for more advanced, interesting future scenarios could be lost or at least reduced.
So, although it may not be seen as visionary or exciting, I believe that the "killer apps" for Bluetooth wireless communication will be those simple things such as cable replacement that the technology already enables. also I believe that it is important to do these things well, especially in the areas of interoperability and ease of use.