This is just in case anyone else is wondering how to implement signalling for OpenTok on Android.
When I asked Charly about signalling for Android he pointed me towards Push or Parse which are third party APIs. Although both of those look really amazing, I ended up getting signalling implemented splendidly using Google Cloud Messaging... for free. Although it's mostly used by devs for push notifications, because GCMs carry a payload with them they can really be used for whatever you want including signalling for OpenTok. Just throwing it out there....