--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/doc/SIM-in-Calypso-phone	Sun Mar 21 05:04:33 2021 +0000
@@ -0,0 +1,21 @@
+fc-simtool can operate on SIM cards that sit inside a Calypso phone or FC
+development board, as opposed to the more classic case of operating on a SIM
+inserted into a dedicated card reading/programming station.  However, this
+special Calypso mode of operation works in an unusual way: instead of invoking
+fc-simtool (or fc-uicc-tool) directly, you have to run a front end program
+called fc-simint.  fc-simint loads and runs simagent on the Calypso device the
+same way how fc-loadtool loads and runs loadagent, then it passes the open file
+descriptor to fc-simtool via the special internal-use-only -C option.
+
+fc-simint and its simagent back end reside in the FreeCalypso host tools
+package, not in FC SIM tools.  As of this writing, a packaged release of FC
+host tools with fc-simint and simagent.srec included has not been produced yet.
+A new fc-host-tools-r15 release is planned for the near future; if you need to
+use the new feature right now and can't wait for the upcoming release, you will
+need to get the current code from the Hg repository:
+
+https://www.freecalypso.org/hg/freecalypso-tools/
+
+Please beware that if you are not able to wait for the upcoming release, you
+will have to install the special ARM7 gcc toolchain and compile simagent
+(Calypso target code piece) from source.