diff --git a/recipes-connectivity/ublox-gsm-config/files/sim.conf b/recipes-connectivity/ublox-gsm-config/files/sim.conf
index d4b6d96..81ab943 100644
--- a/recipes-connectivity/ublox-gsm-config/files/sim.conf
+++ b/recipes-connectivity/ublox-gsm-config/files/sim.conf
@@ -1,3 +1,15 @@
+#
+# Select the SIM card to be used by the modem
+# This file is part of ublox-gsm-config service
+#
+# auto: The script will detect if a physical SIM card is
+#       present and switch to eSIM if it is not the case
+# main: Use the physical SIM card on the main board
+# esim: Use the eSIM of the main bard
+# ui-top: Use the SIM card that is on top of the User Interface
+# ui-btm: Use the SIM card that is on the bottom of the User Interface
+#
+
 [default]
 #SIM=esim
 #SIM=main