class MyService : IMyContract
{
   [OperationBehavior(TransactionScopeRequired = true)]
   public void MyMethod(...)
   {
      MyClass obj = new MyClass( );
      obj.SomeMethod( );
   }
}
class MyClass
{
   public void SomeMethod( )
   {
      using(TransactionScope scope = new TransactionScope( ))
      {
         //Do some work then
         scope.Complete( );
      }
   }
}

////////////////////////// Service Side ////////////////////////////
[ServiceContract]
interface IMyContract
{
   [OperationContract]
   [TransactionFlow(TransactionFlowOption.Allowed)]
   void MyMethod(...);
}
[ServiceContract]
interface IMyOtherContract
{
   [OperationContract]
   [TransactionFlow(TransactionFlowOption.Mandatory)]
   void MyOtherMethod(...);
}
class MyService : IMyContract
{
   [OperationBehavior(TransactionScopeRequired = true)]
   public void MyMethod(...)
   {...}
}
class MyOtherService : IMyOtherContract
{
   [OperationBehavior(TransactionScopeRequired = true)]
   public void MyOtherMethod(...)
   {...}
}
////////////////////////// Client Side ////////////////////////////
using(TransactionScope scope = new TransactionScope( ))
{
   MyContractClient proxy1 = new MyContractClient( );
   proxy1.MyMethod(...);
   proxy1.Close( );

   MyOtherContractClient proxy2 = new MyOtherContractClient( );
   proxy2.MyOtherMethod(...);
   proxy2.Close( );

   scope.Complete( );
}

//Can combine in single using block:
using(MyContractClient proxy3 = new MyContractClient( ))
using(MyOtherContractClient proxy4 = new MyOtherContractClient( ))
using(TransactionScope scope = new TransactionScope( ))
{
   proxy3.MyMethod(...);
   proxy4.MyOtherMethod(...);
   scope.Complete( );
}