I can't tell if we're thinking the same thing (unfamiliar with LinkedIn's model), but I thought maybe over time some users would emerge as domain experts, and this could be made apparent through some review/karma system. At some point, you could go to a model where to triage calls to those high-value experts, you charge a fee. Perhaps a share of that revenue goes to the expert in demand.

I agree. I also really like every approach that does not discourage relationships being formed and being taken offline or somewhere else :)