Cleanup iOS version for phone service status & document.

ios/Classes/strategies/PhonePermissionStrategy.m

@@ -36,8 +36,6 @@
      * Returns YES if the device can place a phone call
      */
 
-    // Check if the device can place a phone call
-    if ([[UIApplication sharedApplication] canOpenURL:[NSURL URLWithString:@"tel://"]]) {
     // Device supports phone calls, lets confirm it can place one right now
     CTTelephonyNetworkInfo *netInfo = [[CTTelephonyNetworkInfo alloc] init];
     CTCarrier *carrier = [netInfo subscriberCellularProvider];
@@ -49,10 +47,6 @@
         // Device can place a phone call
         return YES;
     }
-    } else {
-        // Device does not support phone calls
-        return  NO;
-    }
 }
 
 @end

lib/src/permission_handler.dart

@@ -42,13 +42,20 @@ class PermissionHandler {
   /// Returns a [Future] containing the current service status for the supplied [PermissionGroup].
   ///
   /// Notes about specific PermissionGroups:
-  /// - **PermissionGroup.phone** on Android:
+  /// - **PermissionGroup.phone**
+  ///   - Android:
   ///     - The method will return [ServiceStatus.notApplicable] when:
   ///       1. the device lacks the TELEPHONY feature
   ///       1. TelephonyManager.getPhoneType() returns PHONE_TYPE_NONE
   ///       1. when no Intents can be resolved to handle the `tel:` scheme
   ///     - The method will return [ServiceStatus.disabled] when:
   ///       1. the SIM card is missing
+  ///   - iOS:
+  ///     - The method will return [ServiceStatus.notApplicable] when:
+  ///       1. the native code can not find a handler for the `tel:` scheme
+  ///     - The method will return [ServiceStatus.disabled] when:
+  ///       1. the mobile network code (MNC) is either 0 or 65535. See
+  ///          https://stackoverflow.com/a/11595365 for details
   ///   - **PLEASE NOTE that this is still not a perfect indication** of the
   ///     devices' capability to place & connect phone calls
   ///     as it also depends on the network condition.