- "requires payment" and "completely anonymously" seem at odds; especially when the person you're communicating with will likely have purchased it from an app store. i understand that there is a way to purchase it with btc at their own site, but that doesn't really help with licencing and GCM

- proper implementation of e2e means where the servers are shouldn't matter

- threema uses GCM too -> whole google play services framework

- this steve gibson? http://attrition.org/errata/charlatan/steve_gibson/