diff --git a/telephony/java/android/telephony/TelephonyManager.java b/telephony/java/android/telephony/TelephonyManager.java
index ee254d7d2b9fb..020fe2e6c9dcc 100644
--- a/telephony/java/android/telephony/TelephonyManager.java
+++ b/telephony/java/android/telephony/TelephonyManager.java
@@ -362,7 +362,6 @@ public class TelephonyManager {
         }
     }
 
-
     /**
      * Returns the number of phones available.
      * Returns 0 if none of voice, sms, data is not supported
@@ -395,6 +394,31 @@ public class TelephonyManager {
         return phoneCount;
     }
 
+    /**
+     *
+     * Return how many phone / logical modem can be active simultaneously, in terms of device
+     * capability.
+     * For example, for a dual-SIM capable device, it always returns 2, even if only one logical
+     * modem / SIM is active (aka in single SIM mode).
+     *
+     * TODO: b/139642279 publicize and rename.
+     * @hide
+     */
+    public static int getMaxPhoneCount() {
+        // TODO: b/139642279 when turning on this feature, remove dependency of
+        // PROPERTY_REBOOT_REQUIRED_ON_MODEM_CHANGE and always return result based on
+        // PROPERTY_MAX_ACTIVE_MODEMS.
+        String rebootRequired = SystemProperties.get(
+                TelephonyProperties.PROPERTY_REBOOT_REQUIRED_ON_MODEM_CHANGE);
+        if (rebootRequired.equals("false")) {
+            // If no reboot is required, return max possible active modems.
+            return SystemProperties.getInt(
+                    TelephonyProperties.PROPERTY_MAX_ACTIVE_MODEMS, getDefault().getPhoneCount());
+        } else {
+            return getDefault().getPhoneCount();
+        }
+    }
+
     /** {@hide} */
     @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
     public static TelephonyManager from(Context context) {
diff --git a/telephony/java/com/android/internal/telephony/TelephonyProperties.java b/telephony/java/com/android/internal/telephony/TelephonyProperties.java
index dd9b2421a333b..bf5c0a18cc964 100644
--- a/telephony/java/com/android/internal/telephony/TelephonyProperties.java
+++ b/telephony/java/com/android/internal/telephony/TelephonyProperties.java
@@ -231,4 +231,11 @@ public interface TelephonyProperties
     String DISPLAY_OPPORTUNISTIC_SUBSCRIPTION_CARRIER_TEXT_PROPERTY_NAME =
             "persist.radio.display_opportunistic_carrier";
 
+    /**
+     * How many logical modems can be active simultaneously. For example, if a device is dual-SIM
+     * capable but currently only one SIM slot and one logical modem is active, this value is still
+     * two.
+     * Type: int
+     */
+    static final String PROPERTY_MAX_ACTIVE_MODEMS = "ro.telephony.max.active.modems";
 }