I think we will have to use wifi.
My thinking was that a new set of messages would come in to my phone, and be compared against those I have. Duplicates would be removed, and any with a sender I subscribe to would be displayed in my feed.
Of course, there would have to be a purging mechanism, and I think stored messages could be culled by date. However, you might do something more interesting, and add the # of hops to each message. Therefore you could cull messages based on date and their # of previous hops. If a message has hopped a lot, it is more likely to have reached its subscribers.
Messages should be short, of course.
I'm sure there has been work done on this type of network. You could probably model it to find the optimal parameters for purging the list. It's almost like a flu.