Winlink (amateur radio e-mail over radio) has been available for Android for a while. It has just become available as a public beta now for iOS too.
It won't only connect via TCP/IP though, it will also pair with a VARA modem or packet KISS modem via WiFi or Bluetooth. RadioMail requires a running instance of VARA modem to be available. For packet mode, Mobilinkd and DireWolf packet modems are both supported.
See
RadioMail#technology #hamradio #amateurradio #Winlink #iOS 
Beautiful amateur radio experience for Winlink email on your iPhone.
