But the network effects are still there if you have an interoperable standard. You can use _any_ app that supports the standard and still connect to everybody in the social network.
There is no reason why the social network of mankind should remain captured in the userbase of a single messaging app. And it is the abstract social network that does provide the network effects.
Did they _really_ try though? Google sometimes fails to appreciate that just "putting it out there" isn't enough.
Funny enough, they also fail to see that forcing people to adopt something doesn't work either. For a company that lives off advertising, they sure don't show much skill at marketing.
There are some technical quirks if it is supposed to be a decentralized system but still tied to your telephone number as account identification/address. You'd obviously want to be as independent as possible from your service provider, especially here in Europe, where it is possible to take the phone number with you when changing providers.
It'd probably have to be a system where the server must verify that the number actually belongs to you by sending you a "traditional" SMS with an access code. You'd also need a trust network among the servers or else there would be servers announcing every telephone number out there as theirs.
Regarding the app, I guess any app that supports the protocol would do, even ones that also do other things. This should produce a healty app ecosystem.
And the carriers charged 20 cents per SMS [1]? Yup, I remember those days. No thanks.
[1] http://gizmodo.com/5832245/atts-new-text-plan-overcharges-yo...