diff --git a/include/asterisk/devicestate.h b/include/asterisk/devicestate.h
index 3226cfcaaa7a5291b60e61433e9208de398ab9bd..ff4cdd40bd936ba82ac1f0bc4d4284660e613ed8 100644
--- a/include/asterisk/devicestate.h
+++ b/include/asterisk/devicestate.h
@@ -58,6 +58,7 @@ enum ast_device_state {
 	AST_DEVICE_RINGING,      /*!< Device is ringing */
 	AST_DEVICE_RINGINUSE,    /*!< Device is ringing *and* in use */
 	AST_DEVICE_ONHOLD,       /*!< Device is on hold */
+	AST_DEVICE_TOTAL,        /*/ Total num of device states, used for testing */
 };
 
 /*! \brief Devicestate provider call back */
@@ -247,6 +248,15 @@ void ast_devstate_aggregate_add(struct ast_devstate_aggregate *agg, enum ast_dev
  */
 enum ast_device_state ast_devstate_aggregate_result(struct ast_devstate_aggregate *agg);
 
+/*!
+ * \brief Map devstate to an extension state.
+ *
+ * \param[in] device state
+ *
+ * \return the extension state mapping.
+ */
+enum ast_extension_states ast_devstate_to_extenstate(enum ast_device_state devstate);
+
 /*!
  * \brief You shouldn't care about the contents of this struct
  *
diff --git a/main/devicestate.c b/main/devicestate.c
index 33159be9b8e3673446d2b0e0a62b17d116209602..01e4b27f5769264be5b43095f5a3cb306a5d2dd5 100644
--- a/main/devicestate.c
+++ b/main/devicestate.c
@@ -746,14 +746,12 @@ void ast_devstate_aggregate_add(struct ast_devstate_aggregate *agg, enum ast_dev
 		break;
 	case AST_DEVICE_INUSE:
 		agg->in_use = 1;
-		agg->all_busy = 0;
 		agg->all_unavail = 0;
 		agg->all_free = 0;
 		agg->all_unknown = 0;
 		break;
 	case AST_DEVICE_RINGING:
 		agg->ring = 1;
-		agg->all_busy = 0;
 		agg->all_unavail = 0;
 		agg->all_free = 0;
 		agg->all_unknown = 0;
@@ -761,7 +759,6 @@ void ast_devstate_aggregate_add(struct ast_devstate_aggregate *agg, enum ast_dev
 	case AST_DEVICE_RINGINUSE:
 		agg->in_use = 1;
 		agg->ring = 1;
-		agg->all_busy = 0;
 		agg->all_unavail = 0;
 		agg->all_free = 0;
 		agg->all_unknown = 0;
@@ -786,43 +783,60 @@ void ast_devstate_aggregate_add(struct ast_devstate_aggregate *agg, enum ast_dev
 		agg->all_free = 0;
 		break;
 	case AST_DEVICE_UNKNOWN:
+		agg->all_busy = 0;
+		agg->all_free = 0;
+		break;
+	case AST_DEVICE_TOTAL: /* not a device state, included for completeness. */
 		break;
 	}
 }
 
-enum ast_device_state ast_devstate_aggregate_result(struct ast_devstate_aggregate *agg)
+enum ast_extension_states ast_devstate_to_extenstate(enum ast_device_state devstate)
 {
-	if (agg->all_unknown) {
-		return AST_DEVICE_UNKNOWN;
+	switch (devstate) {
+	case AST_DEVICE_ONHOLD:
+		return AST_EXTENSION_ONHOLD;
+	case AST_DEVICE_BUSY:
+		return AST_EXTENSION_BUSY;
+	case AST_DEVICE_UNAVAILABLE:
+	case AST_DEVICE_UNKNOWN:
+	case AST_DEVICE_INVALID:
+		return AST_EXTENSION_UNAVAILABLE;
+	case AST_DEVICE_RINGINUSE:
+		return (AST_EXTENSION_INUSE | AST_EXTENSION_RINGING);
+	case AST_DEVICE_RINGING:
+		return AST_EXTENSION_RINGING;
+	case AST_DEVICE_INUSE:
+		return AST_EXTENSION_INUSE;
+	case AST_DEVICE_NOT_INUSE:
+		return AST_EXTENSION_NOT_INUSE;
+	case AST_DEVICE_TOTAL: /* not a device state, included for completeness */
+		break;
 	}
 
-	if (agg->all_free) {
-		return AST_DEVICE_NOT_INUSE;
-	}
+	return AST_EXTENSION_NOT_INUSE;
+}
 
-	if ((agg->in_use || agg->on_hold) && agg->ring) {
+enum ast_device_state ast_devstate_aggregate_result(struct ast_devstate_aggregate *agg)
+{
+	if (agg->all_free)
+		return AST_DEVICE_NOT_INUSE;
+	if ((agg->in_use || agg->on_hold) && agg->ring)
 		return AST_DEVICE_RINGINUSE;
-	}
-
-	if (agg->all_busy) {
+	if (agg->ring)
+		return AST_DEVICE_RINGING;
+	if (agg->busy)
 		return AST_DEVICE_BUSY;
-	}
-
-	if (agg->in_use) {
+	if (agg->in_use)
 		return AST_DEVICE_INUSE;
-	}
-
-	if (agg->ring) {
-		return AST_DEVICE_RINGING;
-	}
-
-	if (agg->on_hold) {
+	if (agg->on_hold)
 		return AST_DEVICE_ONHOLD;
-	}
-
-	if (agg->all_unavail) {
+	if (agg->all_busy)
+		return AST_DEVICE_BUSY;
+	if (agg->all_unknown)
+		return AST_DEVICE_UNKNOWN;
+	if (agg->all_unavail)
 		return AST_DEVICE_UNAVAILABLE;
-	}
 
 	return AST_DEVICE_NOT_INUSE;
 }
diff --git a/main/pbx.c b/main/pbx.c
index 4d1bfb4935eaebdd2181c3715b80d974839b9c8e..5e31078fe0fdbb386dc648569d81a3636ed85cea 100644
--- a/main/pbx.c
+++ b/main/pbx.c
@@ -22,7 +22,6 @@
  *
  * \author Mark Spencer <markster@digium.com>
  */
-
 #include "asterisk.h"
 
 ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
@@ -4090,7 +4089,6 @@ static int ast_extension_state2(struct ast_exten *e)
 	struct ast_str *hint = ast_str_thread_get(&extensionstate_buf, 16);
 	char *cur, *rest;
 	struct ast_devstate_aggregate agg;
-	enum ast_device_state state;
 
 	if (!e)
 		return -1;
@@ -4105,28 +4103,7 @@ static int ast_extension_state2(struct ast_exten *e)
 		ast_devstate_aggregate_add(&agg, ast_device_state(cur));
 	}
 
-	state = ast_devstate_aggregate_result(&agg);
-
-	switch (state) {
-	case AST_DEVICE_ONHOLD:
-		return AST_EXTENSION_ONHOLD;
-	case AST_DEVICE_BUSY:
-		return AST_EXTENSION_BUSY;
-	case AST_DEVICE_UNAVAILABLE:
-	case AST_DEVICE_UNKNOWN:
-	case AST_DEVICE_INVALID:
-		return AST_EXTENSION_UNAVAILABLE;
-	case AST_DEVICE_RINGINUSE:
-		return (AST_EXTENSION_INUSE | AST_EXTENSION_RINGING);
-	case AST_DEVICE_RINGING:
-		return AST_EXTENSION_RINGING;
-	case AST_DEVICE_INUSE:
-		return AST_EXTENSION_INUSE;
-	case AST_DEVICE_NOT_INUSE:
-		return AST_EXTENSION_NOT_INUSE;
-	}
-
-	return AST_EXTENSION_NOT_INUSE;
+	return ast_devstate_to_extenstate(ast_devstate_aggregate_result(&agg));
 }
 
 /*! \brief Return extension_state as string */
@@ -6459,6 +6436,36 @@ static char *handle_show_globals(struct ast_cli_entry *e, int cmd, struct ast_cl
 	return CLI_SUCCESS;
 }
 
+#ifdef AST_DEVMODE
+static char *handle_show_device2extenstate(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
+{
+	struct ast_devstate_aggregate agg;
+	int i, j, exten, combined;
+
+	switch (cmd) {
+	case CLI_INIT:
+		e->command = "core show device2extenstate";
+		e->usage =
+			"Usage: core show device2extenstate\n"
+			"       Lists device state to extension state combinations.\n";
+	case CLI_GENERATE:
+		return NULL;
+	}
+	for (i = 0; i < AST_DEVICE_TOTAL; i++) {
+		for (j = 0; j < AST_DEVICE_TOTAL; j++) {
+			ast_devstate_aggregate_init(&agg);
+			ast_devstate_aggregate_add(&agg, i);
+			ast_devstate_aggregate_add(&agg, j);
+			combined = ast_devstate_aggregate_result(&agg);
+			exten = ast_devstate_to_extenstate(combined);
+			ast_cli(a->fd, "\n Exten:%14s  CombinedDevice:%12s  Dev1:%12s  Dev2:%12s", ast_extension_state2str(exten), ast_devstate_str(combined), ast_devstate_str(j), ast_devstate_str(i));
+		}
+	}
+	ast_cli(a->fd, "\n");
+	return CLI_SUCCESS;
+}
+#endif
+
 /*! \brief CLI support for listing chanvar's variables in a parseable way */
 static char *handle_show_chanvar(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
 {
@@ -6620,6 +6627,9 @@ static struct ast_cli_entry pbx_cli[] = {
 	AST_CLI_DEFINE(handle_show_hints, "Show dialplan hints"),
 	AST_CLI_DEFINE(handle_show_hint, "Show dialplan hint"),
 	AST_CLI_DEFINE(handle_show_globals, "Show global dialplan variables"),
+#ifdef AST_DEVMODE
+	AST_CLI_DEFINE(handle_show_device2extenstate, "Show expected exten state from multiple device states"),
+#endif
 	AST_CLI_DEFINE(handle_show_chanvar, "Show channel variables"),
 	AST_CLI_DEFINE(handle_show_function, "Describe a specific dialplan function"),
 	AST_CLI_DEFINE(handle_show_application, "Describe a specific dialplan application"),