I think the proper approach to something like this would be to build a social network and then introduce the device, not the other way round. You can't expect users to flock when the barrier to entry is the price of a device and the success of the network is questionable at best. If Facebook made a deal with a mobile device company (say HTC) and made a similar product, they'd be oodles more successful. Although the fact that our phones nowadays support apps and can browse the web makes this sort of moot anyway.