What's the best way to store data that one iOS app sends to another?

[Geoff Canyon]

Each instance of my iOS app needs to maintain a list of other users of the app and be able to send them information, and retrieve information they have sent. Think email, but without the image, attachment, etc. overhead -- more like sending tweets as emails. What sort of host/infrastructure would work for this? It might be a hosted database, in which case is there one that is easier to use with LC? Or it might just be a hosted file system, in which case how might I handle security?