diff --git a/plugins/atgen.c b/plugins/atgen.c
index 1ce2467a..413e8a3f 100644
--- a/plugins/atgen.c
+++ b/plugins/atgen.c
@@ -78,7 +78,9 @@ static void atgen_remove(struct ofono_modem *modem)
 
 static void atgen_debug(const char *str, void *user_data)
 {
-	ofono_info("%s", str);
+	const char *prefix = user_data;
+
+	ofono_info("%s%s", prefix, str);
 }
 
 static int atgen_enable(struct ofono_modem *modem)
@@ -140,7 +142,7 @@ static int atgen_enable(struct ofono_modem *modem)
 		return -ENOMEM;
 
 	if (getenv("OFONO_AT_DEBUG"))
-		g_at_chat_set_debug(chat, atgen_debug, NULL);
+		g_at_chat_set_debug(chat, atgen_debug, "");
 
 	ofono_modem_set_data(modem, chat);
 
diff --git a/plugins/calypso.c b/plugins/calypso.c
index a2d4ec82..8c54d5ec 100644
--- a/plugins/calypso.c
+++ b/plugins/calypso.c
@@ -90,21 +90,18 @@ struct calypso_data {
 static const char *cpin_prefix[] = { "+CPIN:", NULL };
 static const char *none_prefix[] = { NULL };
 
-static void calypso_debug(const char *str, void *data)
+static void calypso_dlc_debug(const char *str, void *user_data)
 {
-	guint dlc = GPOINTER_TO_UINT(data);
+	guint dlc = GPOINTER_TO_UINT(user_data);
 
 	ofono_info("DLC%u: %s", dlc, str);
 }
 
-static void calypso_mux_debug(const char *str, void *data)
+static void calypso_debug(const char *str, void *user_data)
 {
-	ofono_info("MUX: %s", str);
-}
+	const char *prefix = user_data;
 
-static void calypso_setup_debug(const char *str, void *data)
-{
-	ofono_info("Setup: %s", str);
+	ofono_info("%s%s", prefix, str);
 }
 
 static int calypso_probe(struct ofono_modem *modem)
@@ -272,7 +269,7 @@ static void mux_setup(GAtMux *mux, gpointer user_data)
 	data->mux = mux;
 
 	if (getenv("OFONO_AT_DEBUG"))
-		g_at_mux_set_debug(data->mux, calypso_mux_debug, NULL);
+		g_at_mux_set_debug(data->mux, calypso_debug, "MUX: ");
 
 	g_at_mux_start(mux);
 
@@ -285,7 +282,7 @@ static void mux_setup(GAtMux *mux, gpointer user_data)
 		g_io_channel_unref(io);
 
 		if (getenv("OFONO_AT_DEBUG"))
-			g_at_chat_set_debug(data->dlcs[i], calypso_debug,
+			g_at_chat_set_debug(data->dlcs[i], calypso_dlc_debug,
 						GUINT_TO_POINTER(i));
 
 		g_at_chat_set_wakeup_command(data->dlcs[i], "AT\r", 500, 5000);
@@ -336,7 +333,7 @@ static void modem_initialize(struct ofono_modem *modem)
 		goto error;
 
 	if (getenv("OFONO_AT_DEBUG") != NULL)
-		g_at_chat_set_debug(chat, calypso_setup_debug, NULL);
+		g_at_chat_set_debug(chat, calypso_debug, "Setup: ");
 
 	g_at_chat_set_wakeup_command(chat, "AT\r", 500, 5000);
 
diff --git a/plugins/g1.c b/plugins/g1.c
index fa96eb1e..0cbecef1 100644
--- a/plugins/g1.c
+++ b/plugins/g1.c
@@ -50,9 +50,11 @@
 
 #include <drivers/atmodem/vendor.h>
 
-static void g1_debug(const char *str, void *data)
+static void g1_debug(const char *str, void *user_data)
 {
-	ofono_info("%s", str);
+	const char *prefix = user_data;
+
+	ofono_info("%s%s", prefix, str);
 }
 
 /* Detect hardware, and initialize if found */
@@ -111,8 +113,8 @@ static int g1_enable(struct ofono_modem *modem)
 	if (chat == NULL)
 		return -EIO;
 
-	if (getenv("OFONO_AT_DEBUG") != NULL)
-		g_at_chat_set_debug(chat, g1_debug, NULL);
+	if (getenv("OFONO_AT_DEBUG"))
+		g_at_chat_set_debug(chat, g1_debug, "");
 
 	ofono_modem_set_data(modem, chat);
 
diff --git a/plugins/hfp.c b/plugins/hfp.c
index 9a892db7..62d884be 100644
--- a/plugins/hfp.c
+++ b/plugins/hfp.c
@@ -66,7 +66,9 @@ static GHashTable *modem_hash = NULL;
 
 static void hfp_debug(const char *str, void *user_data)
 {
-	ofono_info("%s", str);
+	const char *prefix = user_data;
+
+	ofono_info("%s%s", prefix, str);
 }
 
 static void clear_data(struct ofono_modem *modem)
@@ -337,7 +339,7 @@ static int service_level_connection(struct ofono_modem *modem, int fd)
 	g_at_chat_set_disconnect_function(chat, hfp_disconnected_cb, modem);
 
 	if (getenv("OFONO_AT_DEBUG"))
-		g_at_chat_set_debug(chat, hfp_debug, NULL);
+		g_at_chat_set_debug(chat, hfp_debug, "");
 
 	snprintf(buf, sizeof(buf), "AT+BRSF=%d", data->hf_features);
 	g_at_chat_send(chat, buf, brsf_prefix,
diff --git a/plugins/hso.c b/plugins/hso.c
index bfc5c471..055c63b3 100644
--- a/plugins/hso.c
+++ b/plugins/hso.c
@@ -86,6 +86,7 @@ static void hso_remove(struct ofono_modem *modem)
 static void hso_debug(const char *str, void *user_data)
 {
 	const char *prefix = user_data;
+
 	ofono_info("%s%s", prefix, str);
 }
 
@@ -157,7 +158,7 @@ static int hso_enable(struct ofono_modem *modem)
 		return -EIO;
 
 	if (getenv("OFONO_AT_DEBUG"))
-		g_at_chat_set_debug(data->control, hso_debug, "Control:");
+		g_at_chat_set_debug(data->control, hso_debug, "Control: ");
 
 	data->app = create_port(app);
 
@@ -169,7 +170,7 @@ static int hso_enable(struct ofono_modem *modem)
 	}
 
 	if (getenv("OFONO_AT_DEBUG"))
-		g_at_chat_set_debug(data->app, hso_debug, "App:");
+		g_at_chat_set_debug(data->app, hso_debug, "App: ");
 
 	g_at_chat_send(data->control, "ATE0", none_prefix, NULL, NULL, NULL);
 	g_at_chat_send(data->app, "ATE0", none_prefix, NULL, NULL, NULL);
diff --git a/plugins/huawei.c b/plugins/huawei.c
index 27473a8d..dd24c3c5 100644
--- a/plugins/huawei.c
+++ b/plugins/huawei.c
@@ -115,6 +115,7 @@ static void huawei_remove(struct ofono_modem *modem)
 static void huawei_debug(const char *str, void *user_data)
 {
 	const char *prefix = user_data;
+
 	ofono_info("%s%s", prefix, str);
 }
 
@@ -528,7 +529,7 @@ static void huawei_disconnect(gpointer user_data)
 	g_at_chat_unref(data->modem);
 	data->modem = NULL;
 
-	data->modem = open_device(modem, "Modem", "Modem:");
+	data->modem = open_device(modem, "Modem", "Modem: ");
 	if (data->modem == NULL)
 		return;
 
@@ -553,14 +554,14 @@ static int huawei_enable(struct ofono_modem *modem)
 
 	DBG("%p", modem);
 
-	data->modem = open_device(modem, "Modem", "Modem:");
+	data->modem = open_device(modem, "Modem", "Modem: ");
 	if (data->modem == NULL)
 		return -EINVAL;
 
 	g_at_chat_set_disconnect_function(data->modem,
 						huawei_disconnect, modem);
 
-	data->pcui = open_device(modem, "Pcui", "Pcui:");
+	data->pcui = open_device(modem, "Pcui", "PCUI: ");
 	if (data->pcui == NULL) {
 		g_at_chat_unref(data->modem);
 		data->modem = NULL;
diff --git a/plugins/mbm.c b/plugins/mbm.c
index a706a34c..41c96384 100644
--- a/plugins/mbm.c
+++ b/plugins/mbm.c
@@ -103,7 +103,7 @@ static void mbm_debug(const char *str, void *user_data)
 {
 	const char *prefix = user_data;
 
-	ofono_info("%s %s", prefix, str);
+	ofono_info("%s%s", prefix, str);
 }
 
 static gboolean init_simpin_check(gpointer user_data);
@@ -316,7 +316,7 @@ static int mbm_enable(struct ofono_modem *modem)
 		return -EIO;
 
 	if (getenv("OFONO_AT_DEBUG"))
-		g_at_chat_set_debug(data->modem_port, mbm_debug, "Modem:");
+		g_at_chat_set_debug(data->modem_port, mbm_debug, "Modem: ");
 
 	data->data_port = create_port(data_dev);
 
@@ -328,7 +328,7 @@ static int mbm_enable(struct ofono_modem *modem)
 	}
 
 	if (getenv("OFONO_AT_DEBUG"))
-		g_at_chat_set_debug(data->data_port, mbm_debug, "Data:");
+		g_at_chat_set_debug(data->data_port, mbm_debug, "Data: ");
 
 	g_at_chat_register(data->modem_port, "*EMRDY:", emrdy_notifier,
 					FALSE, modem, NULL);
diff --git a/plugins/nokia.c b/plugins/nokia.c
index b7db2cc9..f65617be 100644
--- a/plugins/nokia.c
+++ b/plugins/nokia.c
@@ -87,6 +87,7 @@ static void nokia_remove(struct ofono_modem *modem)
 static void nokia_debug(const char *str, void *user_data)
 {
         const char *prefix = user_data;
+
         ofono_info("%s%s", prefix, str);
 }
 
@@ -134,7 +135,7 @@ static void nokia_disconnect(gpointer user_data)
 	g_at_chat_unref(data->modem);
 	data->modem = NULL;
 
-	data->modem = open_device(modem, "Modem", "Modem:");
+	data->modem = open_device(modem, "Modem", "Modem: ");
 	if (!data->modem)
 		return;
 
@@ -164,14 +165,14 @@ static int nokia_enable(struct ofono_modem *modem)
 
 	DBG("%p", modem);
 
-	data->modem = open_device(modem, "Modem", "Modem:");
+	data->modem = open_device(modem, "Modem", "Modem: ");
 	if (data->modem == NULL)
 		return -EINVAL;
 
 	g_at_chat_set_disconnect_function(data->modem,
 						nokia_disconnect, modem);
 
-	data->control = open_device(modem, "Control", "Control:");
+	data->control = open_device(modem, "Control", "Control: ");
 	if (data->control == NULL) {
 		g_at_chat_unref(data->modem);
 		data->modem = NULL;
diff --git a/plugins/novatel.c b/plugins/novatel.c
index 51360abc..4a3802e8 100644
--- a/plugins/novatel.c
+++ b/plugins/novatel.c
@@ -89,6 +89,7 @@ static void novatel_remove(struct ofono_modem *modem)
 static void novatel_debug(const char *str, void *user_data)
 {
 	const char *prefix = user_data;
+
 	ofono_info("%s%s", prefix, str);
 }
 
@@ -144,7 +145,7 @@ static void nwdmat_action(gboolean ok, GAtResult *result, gpointer user_data)
 
 	data->dmat_mode = 1;
 
-	data->secondary = open_device(modem, "SecondaryDevice", "2nd:");
+	data->secondary = open_device(modem, "SecondaryDevice", "Control: ");
 	if (!data->secondary)
 		goto done;
 
@@ -206,7 +207,7 @@ static void novatel_disconnect(gpointer user_data)
 	g_at_chat_unref(data->primary);
 	data->primary = NULL;
 
-	data->primary = open_device(modem, "PrimaryDevice", "1st:");
+	data->primary = open_device(modem, "PrimaryDevice", "Modem: ");
 	if (!data->primary)
 		return;
 
@@ -228,7 +229,7 @@ static int novatel_enable(struct ofono_modem *modem)
 
 	DBG("%p", modem);
 
-	data->primary = open_device(modem, "PrimaryDevice", "1st:");
+	data->primary = open_device(modem, "PrimaryDevice", "Modem: ");
 	if (!data->primary)
 		return -EIO;
 
diff --git a/plugins/palmpre.c b/plugins/palmpre.c
index 7d2aeb43..17148637 100644
--- a/plugins/palmpre.c
+++ b/plugins/palmpre.c
@@ -79,7 +79,9 @@ static void palmpre_remove(struct ofono_modem *modem)
 
 static void palmpre_debug(const char *str, void *user_data)
 {
-	ofono_info("%s", str);
+	const char *prefix = user_data;
+
+	ofono_info("%s%s", prefix, str);
 }
 
 static void cfun_set_on_cb(gboolean ok, GAtResult *result, gpointer user_data)
@@ -126,7 +128,7 @@ static int palmpre_enable(struct ofono_modem *modem)
 		return -ENOMEM;
 
 	if (getenv("OFONO_AT_DEBUG"))
-		g_at_chat_set_debug(data->chat, palmpre_debug, NULL);
+		g_at_chat_set_debug(data->chat, palmpre_debug, "");
 
 	/* Ensure terminal is in a known state */
 	g_at_chat_send(data->chat, "ATZ E0 +CMEE=1", NULL, NULL, NULL, NULL);
diff --git a/plugins/ste.c b/plugins/ste.c
index aab07041..508ad587 100644
--- a/plugins/ste.c
+++ b/plugins/ste.c
@@ -106,7 +106,9 @@ static void ste_remove(struct ofono_modem *modem)
 
 static void ste_debug(const char *str, void *user_data)
 {
-	ofono_info("%s", str);
+	const char *prefix = user_data;
+
+	ofono_info("%s%s", prefix, str);
 }
 
 static gboolean init_simpin_check(gpointer user_data);
@@ -235,7 +237,7 @@ static int ste_enable(struct ofono_modem *modem)
 		return -ENOMEM;
 
 	if (getenv("OFONO_AT_DEBUG"))
-		g_at_chat_set_debug(data->chat, ste_debug, NULL);
+		g_at_chat_set_debug(data->chat, ste_debug, "");
 
 	g_at_chat_send(data->chat, "AT&F E0 V1 X4 &C1 +CMEE=1",
 			NULL, NULL, NULL, NULL);
diff --git a/plugins/wavecom.c b/plugins/wavecom.c
index 77b7aa16..73fa502c 100644
--- a/plugins/wavecom.c
+++ b/plugins/wavecom.c
@@ -62,7 +62,9 @@ static void wavecom_remove(struct ofono_modem *modem)
 
 static void wavecom_debug(const char *str, void *user_data)
 {
-	ofono_info("%s", str);
+	const char *prefix = user_data;
+
+	ofono_info("%s%s", prefix, str);
 }
 
 static int wavecom_enable(struct ofono_modem *modem)
@@ -110,7 +112,7 @@ static int wavecom_enable(struct ofono_modem *modem)
 		return -ENOMEM;
 
 	if (getenv("OFONO_AT_DEBUG"))
-		g_at_chat_set_debug(chat, wavecom_debug, NULL);
+		g_at_chat_set_debug(chat, wavecom_debug, "");
 
 	ofono_modem_set_data(modem, chat);
 
diff --git a/plugins/zte.c b/plugins/zte.c
index c82b2b51..07f84665 100644
--- a/plugins/zte.c
+++ b/plugins/zte.c
@@ -89,6 +89,7 @@ static void zte_remove(struct ofono_modem *modem)
 static void zte_debug(const char *str, void *user_data)
 {
         const char *prefix = user_data;
+
         ofono_info("%s%s", prefix, str);
 }
 
@@ -136,7 +137,7 @@ static void zte_disconnect(gpointer user_data)
 	g_at_chat_unref(data->modem);
 	data->modem = NULL;
 
-	data->modem = open_device(modem, "Modem", "Modem:");
+	data->modem = open_device(modem, "Modem", "Modem: ");
 	if (!data->modem)
 		return;
 
@@ -166,14 +167,14 @@ static int zte_enable(struct ofono_modem *modem)
 
 	DBG("%p", modem);
 
-	data->modem = open_device(modem, "Modem", "Modem:");
+	data->modem = open_device(modem, "Modem", "Modem: ");
 	if (data->modem == NULL)
 		return -EINVAL;
 
 	g_at_chat_set_disconnect_function(data->modem,
 						zte_disconnect, modem);
 
-	data->aux = open_device(modem, "Aux", "Aux:");
+	data->aux = open_device(modem, "Aux", "Aux: ");
 	if (data->aux == NULL) {
 		g_at_chat_unref(data->modem);
 		data->modem = NULL;