diff --git a/drivers/modem/gsm_ppp.c b/drivers/modem/gsm_ppp.c
index c1f8fde938b..30884249efa 100644
--- a/drivers/modem/gsm_ppp.c
+++ b/drivers/modem/gsm_ppp.c
@@ -317,6 +317,30 @@ static void gsm_finalize_connection(struct gsm_modem *gsm)
 	}
 
 	set_ppp_carrier_on(gsm);
+
+	if (IS_ENABLED(CONFIG_GSM_MUX) && gsm->mux_enabled) {
+		/* Re-use the original iface for AT channel */
+		ret = modem_iface_uart_init_dev(&gsm->context.iface,
+						gsm->at_dev->config->name);
+		if (ret < 0) {
+			LOG_DBG("iface %suart error %d", "AT ", ret);
+		} else {
+			/* Do a test and try to send AT command to modem */
+			ret = modem_cmd_send(&gsm->context.iface,
+					     &gsm->context.cmd_handler,
+					     &response_cmds[0],
+					     ARRAY_SIZE(response_cmds),
+					     "AT", &gsm->sem_response,
+					     GSM_CMD_AT_TIMEOUT);
+			if (ret < 0) {
+				LOG_DBG("modem setup returned %d, %s",
+					ret, "AT cmds failed");
+			} else {
+				LOG_INF("AT channel %d connected to %s",
+					DLCI_AT, gsm->at_dev->config->name);
+			}
+		}
+	}
 }
 
 static int mux_enable(struct gsm_modem *gsm)
@@ -455,16 +479,23 @@ static void mux_setup(struct k_work *work)
 		break;
 
 	case STATE_DONE:
-		/* Re-use the original iface for AT channel */
-		ret = modem_iface_uart_init(&gsm->context.iface,
-					    &gsm->gsm_data,
-					    gsm->at_dev->config->name);
+		/* At least the SIMCOM modem expects that the Internet
+		 * connection is created in PPP channel. We will need
+		 * to attach the AT channel to context iface after the
+		 * PPP connection is established in order to give AT commands
+		 * to the modem.
+		 */
+		ret = modem_iface_uart_init_dev(&gsm->context.iface,
+						gsm->ppp_dev->config->name);
 		if (ret < 0) {
-			LOG_DBG("iface %suart error %d", "mux ", ret);
+			LOG_DBG("iface %suart error %d", "PPP ", ret);
 			gsm->mux_enabled = false;
 			goto fail;
 		}
 
+		LOG_INF("PPP channel %d connected to %s",
+			DLCI_PPP, gsm->ppp_dev->config->name);
+
 		gsm_finalize_connection(gsm);
 		break;
 	}
diff --git a/drivers/modem/modem_iface_uart.c b/drivers/modem/modem_iface_uart.c
index 15d731f81b4..8b57cb3f30c 100644
--- a/drivers/modem/modem_iface_uart.c
+++ b/drivers/modem/modem_iface_uart.c
@@ -121,27 +121,15 @@ static int modem_iface_uart_write(struct modem_iface *iface,
 	return 0;
 }
 
-int modem_iface_uart_init(struct modem_iface *iface,
-			  struct modem_iface_uart_data *data,
-			  const char *dev_name)
+int modem_iface_uart_init_dev(struct modem_iface *iface,
+			      const char *dev_name)
 {
-	if (!iface || !data) {
-		return -EINVAL;
-	}
-
 	/* get UART device */
 	iface->dev = device_get_binding(dev_name);
 	if (!iface->dev) {
 		return -ENODEV;
 	}
 
-	iface->iface_data = data;
-	iface->read = modem_iface_uart_read;
-	iface->write = modem_iface_uart_write;
-
-	ring_buf_init(&data->rx_rb, data->rx_rb_buf_len, data->rx_rb_buf);
-	k_sem_init(&data->rx_sem, 0, 1);
-
 	uart_irq_rx_disable(iface->dev);
 	uart_irq_tx_disable(iface->dev);
 	modem_iface_uart_flush(iface);
@@ -150,3 +138,33 @@ int modem_iface_uart_init(struct modem_iface *iface,
 
 	return 0;
 }
+
+int modem_iface_uart_init(struct modem_iface *iface,
+			  struct modem_iface_uart_data *data,
+			  const char *dev_name)
+{
+	int ret;
+
+	if (!iface || !data) {
+		return -EINVAL;
+	}
+
+	iface->iface_data = data;
+	iface->read = modem_iface_uart_read;
+	iface->write = modem_iface_uart_write;
+
+	ring_buf_init(&data->rx_rb, data->rx_rb_buf_len, data->rx_rb_buf);
+	k_sem_init(&data->rx_sem, 0, 1);
+
+	/* get UART device */
+	ret = modem_iface_uart_init_dev(iface, dev_name);
+	if (ret < 0) {
+		iface->iface_data = NULL;
+		iface->read = NULL;
+		iface->write = NULL;
+
+		return ret;
+	}
+
+	return 0;
+}
diff --git a/drivers/modem/modem_iface_uart.h b/drivers/modem/modem_iface_uart.h
index 40cf4439e7a..d0b918ab016 100644
--- a/drivers/modem/modem_iface_uart.h
+++ b/drivers/modem/modem_iface_uart.h
@@ -35,6 +35,19 @@ struct modem_iface_uart_data {
 	struct k_sem rx_sem;
 };
 
+/**
+ * @brief  Init modem interface device for UART
+ *
+ * @details This can be called after the init if the UART is changed.
+ *
+ * @param  *iface: modem interface to initialize.
+ * @param  *dev_name: name of the UART device to use
+ *
+ * @retval 0 if ok, < 0 if error.
+ */
+int modem_iface_uart_init_dev(struct modem_iface *iface,
+			      const char *dev_name);
+
 /**
  * @brief  Init modem interface for UART
  *