OpenAPRS, PocketPacket and iAPRS work in iOS.
Couldn't tell you how any of them work I'm still married to the Nokia flip phone 'ecosystem'. Hi-hi.
I also stand corrected, apparently the G6 does work with TinyTrak4 TNCs (and maybe others). It actually sounds as though the G6 needs the TT4 to work fully even with Kenwood radios.
Adding Capability with the Byonics Tiny Tracker 4
The Byonics Tiny Tracker 4 (TT4) is an APRS capable TNC available as a kit or built and tested. It is supported by a host of available interface cables for computer and radio, free downloadable firmware, keyboard and display options, and downloadable documentation. The TT4 is a relatively inexpensive way to turn any 2 meter radio into an APRS station.
While the AvMap GeoSat 6 APRS is designed to work with all Kenwood APRS capable radios, Kenwood does not support all of the messaging capabilities of the G6. Kenwood does support message sending via the mic keypad, only. With a capable TNC such as the TT4 connected between the G6 and your radio, it is possible to select a received station from the G6 APRS contact list and send that station a message. When such a station is selected a soft key board appears on the screen. The “keys” are about the size of my finger tips and make message creation as easy as one could imagine. The G6 keeps a log of messages sent, received, and pending, much like an email application.