I dont think you can receive messages at server level, this is not the point in push notifications. if you want to send information to the service from the app, i would suggest writing a webservice. i've implemented this myself, and had to do a little digging to find some code that could communicate with the webservice as it was written in c# and the app was java, but i can paste some code that might help if you think that would help you communicate.
Long story short though, if you want an app to talk to a server, then write a web service. if you want a server to talk to an app, use push notifications.