.NET 4.0 - C# Application needs to pull messages out of Exchange Server 2007. We are using EWS Managed API 1.0. Also the app needs to push messages to the Exchange Server 2007.
Pull subscriptions can be implemented directly with the managed API.
For push subscriptions, have a look at http://exchangenotification.codeplex.com/. I've created a .NET Wrapper for push notifications, which is rather simple to use.