IIRC, there are already apps in Google's App Store that will talk to rtl_tcp servers (and using a server will save the battery on your Android device). They were available many years ago. I had to write my own iPhone app because (at the time I started) there were none that would talk to my SDRs. Since then I've been gradually adding support for Airspy HF+, LimeSDR, Hermes Lite 2, and currently testing with the 16-bit Red Pitaya. Lots of cool SDRs (and new iOS devices as well).
