Seems likely to me. I guess the issue is the lack of 'openness' to these systems. Something that various people (e.g. Google) are trying to do something about (and profit from it). I'm unlikely to add my parents to Facebook to get them on my phone, for example. Equally, people I work with won't necessarily be on Facebook but might be on LinkedIn or similar. Phones that work with just Facebook are going to be strictly targeted at 15-21 year olds I think...

I can do Facebook on my iPhone, and that works pretty well. Not that I use it much, I imagine heavy users would like a well made app integrated well into a phone...