I'm not an Android developer so I hope my mental picture of what GCM does isn't off. > My sense is that this isn't because you find the communication over GCM

I'm not an Android developer so I hope my mental picture of what GCM does isn't off. > My sense is that this isn't because you find the communication over GCM to be inherently offensive (it's just a tickle, after all), Using GCM still means that Google could suddenly stop to relay the messages for some users, right? (Say, those who seem to be using a non-official reimplementation of GCM...). Then the service would suddenly stop working for these users. So I'd still rather be able to avoid relying on the GCM backend at all, if that's possible. > What I don't understand is why nobody just writes an API-compatible open source implementation of play services Couldn't the Play Services API change without warning? It is sensibly designed so another implementation wouldn't be too hackish? People shouldn't have to reimplement such things by mimicking Google's API. In principle, there should be a documented and stable standard, not hacky reimplementations. I agree, though, that probably the way to go would be to first build a different messaging system like this (maybe using XMPP as a backend?).