Unfortunately at least on iOS, it's always going to be severely limited by what Apple allows and does not allow apps to do in the background and with regards to P2P connecting to other (especially non-Apple) Wi-Fi devices.
I've been dreaming about an optionally P2P messenger for a long time, i.e. something that just communicates over the internet while it's there, but lets messages piggy back onto others' devices if not.
This could address simple cases like one person with and another without a mobile data plan, or something more complicated like a hiker passing through a campsite, collecting everybody's pending outgoing messages and submitting them once they have signal again. (The return path in the latter scenario would be much more complicated, as it would require either a lot of storage and broadcasting, or good heuristics about who's going to pass by where, in order to preemptively download messages.)
Unfortunately at least on iOS, it's always going to be severely limited by what Apple allows and does not allow apps to do in the background and with regards to P2P connecting to other (especially non-Apple) Wi-Fi devices.
I've been dreaming about an optionally P2P messenger for a long time, i.e. something that just communicates over the internet while it's there, but lets messages piggy back onto others' devices if not.
This could address simple cases like one person with and another without a mobile data plan, or something more complicated like a hiker passing through a campsite, collecting everybody's pending outgoing messages and submitting them once they have signal again. (The return path in the latter scenario would be much more complicated, as it would require either a lot of storage and broadcasting, or good heuristics about who's going to pass by where, in order to preemptively download messages.)