Pi3 + screen + 20ah lipo + mic + speaker + usb 4g modem (removable)

and linfone or equivelent.

Just need a 3d printer so i can print the case. A bit of a brick. but a quite the "swiss army knife" of comms.

I also dont know how many people are aware just how sensitive the mic is on modern phones. I wrote a little app that turns android phones into bugs (broadcasts sound from the mic over wifi) a few years ago. It can pick up a whisper from 40m away, while when using it as a phone there is never any background noise.