diff --git a/csharp/PhoneNumbers/PhoneNumberUtil.cs b/csharp/PhoneNumbers/PhoneNumberUtil.cs
index 79ce721a..b4d32300 100644
--- a/csharp/PhoneNumbers/PhoneNumberUtil.cs
+++ b/csharp/PhoneNumbers/PhoneNumberUtil.cs
@@ -869,8 +869,10 @@ public static string GetCountryMobileToken(int countryCallingCode)
         /// should be stripped from the number. If this is false, they
         /// will be left unchanged in the number.</param>
         /// <returns>The normalized string version of the phone number.</returns>
+#if !(NET5_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER)
         private static string NormalizeHelper(string number, Func<char, char> normalizationReplacements, bool removeNonMatches)
             => NormalizeHelper(new StringBuilder(number), normalizationReplacements, removeNonMatches).ToString();
+#endif
 
         private static StringBuilder NormalizeHelper(StringBuilder number, Func<char, char> normalizationReplacements, bool removeNonMatches)
         {
@@ -985,27 +987,26 @@ private static bool DescHasData(PhoneNumberDesc desc)
                    || desc.HasNationalNumberPattern;
         }
 
+        // Pre-filtered: excludes FIXED_LINE_OR_MOBILE (convenience aggregate) and UNKNOWN (non-type).
+        private static readonly PhoneNumberType[] s_checkablePhoneNumberTypes =
+        [
+            PhoneNumberType.FIXED_LINE, PhoneNumberType.MOBILE, PhoneNumberType.TOLL_FREE,
+            PhoneNumberType.PREMIUM_RATE, PhoneNumberType.SHARED_COST, PhoneNumberType.VOIP,
+            PhoneNumberType.PERSONAL_NUMBER, PhoneNumberType.PAGER, PhoneNumberType.UAN,
+            PhoneNumberType.VOICEMAIL,
+        ];
+
         /// <summary>
         /// Returns the types we have metadata for based on the PhoneMetadata object passed in, which must
         /// be non-null.
         /// </summary>
-        /// <param name="metadata"></param>
-        /// <returns></returns>
         private HashSet<PhoneNumberType> GetSupportedTypesForMetadata(PhoneMetadata metadata)
         {
             var types = new HashSet<PhoneNumberType>();
-            foreach (PhoneNumberType type in Enum.GetValues(typeof(PhoneNumberType)))
+            foreach (var type in s_checkablePhoneNumberTypes)
             {
-                if (type == PhoneNumberType.FIXED_LINE_OR_MOBILE || type == PhoneNumberType.UNKNOWN)
-                {
-                    // Never return FIXED_LINE_OR_MOBILE (it is a convenience type, and represents that a
-                    // particular number type can't be determined) or UNKNOWN (the non-type).
-                    continue;
-                }
                 if (DescHasData(GetNumberDescByType(metadata, type)))
-                {
                     types.Add(type);
-                }
             }
             return types;
         }
@@ -2305,6 +2306,14 @@ private int MaybeExtractCountryCode(string number, PhoneMetadata defaultRegionMe
                 nationalNumber, keepRawInput, phoneNumber);
         }
 
+        private static bool StringBuilderStartsWith(StringBuilder sb, string value)
+        {
+            if (sb.Length < value.Length) return false;
+            for (var i = 0; i < value.Length; i++)
+                if (sb[i] != value[i]) return false;
+            return true;
+        }
+
         // Same as the string overload above, but takes a StringBuilder workspace directly so callers
         // that already hold a StringBuilder can avoid an extra string<->StringBuilder round-trip.
         // The fullNumber buffer is always mutated (Normalize is unconditional, and any leading '+' or
@@ -2355,9 +2364,10 @@ private int MaybeExtractCountryCode(StringBuilder fullNumber, PhoneMetadata defa
                 // before and after.
                 var defaultCountryCode = defaultRegionMetadata.CountryCode;
                 var defaultCountryCodeString = defaultCountryCode.ToString();
-                var normalizedNumber = fullNumber.ToString();
-                if (normalizedNumber.StartsWith(defaultCountryCodeString, StringComparison.Ordinal))
+                // Avoid the ToString() allocation unless the prefix actually matches (common case: it won't).
+                if (StringBuilderStartsWith(fullNumber, defaultCountryCodeString))
                 {
+                    var normalizedNumber = fullNumber.ToString();
                     var potentialNationalNumberString = normalizedNumber.Substring(defaultCountryCodeString.Length);
                     // Use a separate buffer for the strip-CC trial so callers that share fullNumber as
                     // their workspace are not corrupted when this branch decides not to commit.
@@ -2371,7 +2381,7 @@ private int MaybeExtractCountryCode(StringBuilder fullNumber, PhoneMetadata defa
                     var validNumberPattern = generalDesc.GetNationalNumberPattern();
                     if ((!validNumberPattern.IsMatchAll(normalizedNumber) &&
                          validNumberPattern.IsMatchAll(potentialNationalNumberString)) ||
-                        TestNumberLength(normalizedNumber.Length, defaultRegionMetadata) == ValidationResult.TOO_LONG)
+                        TestNumberLength(fullNumber.Length, defaultRegionMetadata) == ValidationResult.TOO_LONG)
                     {
                         nationalNumber.Append(potentialNationalNumberString);
                         if (keepRawInput)
@@ -2529,7 +2539,11 @@ static string MaybeStripExtension(StringBuilder number, string numberString)
             var m = ExtnPattern().Match(numberString);
             // If we find a potential extension, and the number preceding this is a viable number, we assume
             // it is an extension.
+#if NET7_0_OR_GREATER
+            if (m.Success && IsViablePhoneNumberSpan(numberString.AsSpan(0, m.Index)))
+#else
             if (m.Success && IsViablePhoneNumber(numberString.Substring(0, m.Index)))
+#endif
             {
                 // The numbers are captured into groups in the regular expression.
                 for (int i = 1, length = m.Groups.Count; i < length; i++)
diff --git a/csharp/PhoneNumbers/PhoneNumberUtil.net.cs b/csharp/PhoneNumbers/PhoneNumberUtil.net.cs
index e8105231..91d631be 100644
--- a/csharp/PhoneNumbers/PhoneNumberUtil.net.cs
+++ b/csharp/PhoneNumbers/PhoneNumberUtil.net.cs
@@ -606,6 +606,15 @@ private static void NormalizeHelper(ref Span<char> span,
             }
         }
 
+        private static string NormalizeHelper(string number, Func<char, char> normalizationReplacements, bool removeNonMatches)
+        {
+            if (number.Length == 0) return string.Empty;
+            Span<char> result = stackalloc char[number.Length];
+            var resultLength = 0;
+            NormalizeHelper(ref result, ref resultLength, number, normalizationReplacements, removeNonMatches);
+            return new string(result.Slice(0, resultLength));
+        }
+
         private static bool IsValidAlphaPhone(string number)
         {
             for (int alpha = 0, i = 0; i < number.Length; i++)
@@ -750,6 +759,14 @@ private void PrefixNumberWithCountryCallingCode(ref Span<char> span,
                     return;
             }
         }
+
+#if NET7_0_OR_GREATER
+        internal static bool IsViablePhoneNumberSpan(ReadOnlySpan<char> number)
+        {
+            if (number.Length < MIN_LENGTH_FOR_NSN) return false;
+            return ValidPhoneNumber().IsMatch(number);
+        }
+#endif
     }
 }
 #endif