Photon provides a Unity3D Plugin for Networking
Photon recently released their PUN plugin for Unity3D that allows the “Free” user to implement networking in their game. To extend to Android requires purchase of the PUN+ ($95).
PUN initially works with the Photon Cloud service that provides a pipeline for the data. There is no back-end to the cloud server. The client must have the world and any prefabs that get instantiated at run-time. Thus there is NO persistence. However, with the Photon Server, one can develop some back-end server side scripts that provide world persistence.
Photon can be found here:
Jim in the Matrix 
I’m using Photon cloud in my game. So easy to use, definitely recommended! 😉