Phone number with equality

PhoneNumber.cs

using System;
using System.Globalization;

namespace Taksapp.Domain.ValueObjects
{
    public class PhoneNumber : ValueObject<PhoneNumber>
    {
        public static readonly PhoneNumber NoPhoneNumber = new PhoneNumber();

        public int RegionCode { get; protected set; }
        public string Number { get; protected set; }

        public PhoneNumber(int regionCode, string number)
        {
            if (regionCode < 1 || regionCode > 441624)
                throw new ArgumentOutOfRangeException(nameof(regionCode));
            try
            {
                int.Parse(number, NumberStyles.None);
            }
            catch (Exception e)
            {
                throw new ArgumentException(nameof(number), e);
            }

            RegionCode = regionCode;
            Number = number;
        }

        // For persistence
        protected PhoneNumber()
        {
        }

        protected override bool EqualsCore(PhoneNumber other)
        {
            return RegionCode == other.RegionCode &&
                   Number == other.Number;
        }

        protected override int GetHashCodeCore()
        {
            int hashCode = RegionCode.GetHashCode();
            hashCode = (hashCode * 397) ^ Number.GetHashCode();
            return hashCode;
        }
    }
    
    public abstract class ValueObject<T>
        where T : ValueObject<T>
    {
        public override bool Equals(object obj)
        {
            var valueObject = obj as T;

            if (ReferenceEquals(valueObject, null))
                return false;

            if (GetType() != valueObject.GetType())
                return false;

            return EqualsCore(valueObject);
        }

        public override int GetHashCode()
        {
            return GetHashCodeCore();
        }

        public static bool operator==(ValueObject<T> a, ValueObject<T> b)
        {
            if (ReferenceEquals(a, null) && ReferenceEquals(b, null))
                return true;

            if (ReferenceEquals(a, null) || ReferenceEquals(b, null))
                return false;

            return a.Equals(b);
        }

        public static bool operator!=(ValueObject<T> a, ValueObject<T> b)
        {
            return !(a == b);
        }

        protected abstract bool EqualsCore(T other);

        protected abstract int GetHashCodeCore();
    }
}