I want to build my first Windows Phone 7 application and I'm going to need a service backend.
Should I be using something like NServiceBus? WCF? Any suggestions would be helpful.
I'm guessing the Cloud (Azure) would be the best place to host this service?
NserviceBus I don't think will really help you in this situation.
I would go with WCF hosted in a robust environment. Could be Azure, but doesn't need to be.
Most Importantly though, I think it's all about providing an efficient and intelligent OFFLINE strategy, so your app can still work if services fail. So that would involve efficient syncing and local storage.
For Syncing, check out the MS Sync Framework. Not sure it will work on WP7 yet, but may do at release.
Expect to hear soon about the Sync Framework supporting offline capabilities for Silverlight and Silverlight on Windows Phone 7. As Liam Cavanagh mentions in this blog post before TechEd:
I have a TechEd session this week where I will be demonstrating all of this as well as how we will be extending the capabilities of the sync framework for creating offline applications, specifically allowing Silverlight, Windows Phone 7 and even non-MSFT platforms to be used for the clients.
http://blogs.msdn.com/b/sync/archive/2010/06/07/introducing-data-sync-service-for-sql-azure.aspx