If less than 10 results, we call them two at a time. If more than 10, we call them five at a time. Whoever picks up first is the winner.
This is the simplest possible representation of who is in the call at any one time. We already have a representation of who is online - it looks pretty much like that, but indicates only who is currently in the call.
It would be nice if keywords are additive (ie you narrow down the search by adding keywords).