LA is a sprawling city often suffering significant traffic congestion. Scenes that may take hours RL to pose out - particularly combat scenes, will almost always fully transpire IC in the span of time it would take to respond to a phone call, find car keys, get to a car, and even get to the highway. In short, phoning someone into an unfolding combat-scene is impossible even if they are in an adjacent grid.
On the other hand, we do not want to stifle RP opportunities so logging on or completing one scene and wishing to join in another can suspend a bit of reality, but ONLY at the agreement of those involved. Characters take calculated risks in power use, posturing, and particularly combat based upon those present.
Remember - the theme here tells of isolation and vulnerability and terror - the cavalry is unreliable and distant. Plan aftermath angst scenes rather than piling on your protectors.
Bottom line: A scene can move from casual conversation to 20 rounds of combat faster than anyone can feasibly arrive from even the closest location (e.g., even another building in the same grid room), even with Celerity. Please be reasonable in joining presently-unfolding scenes and confirm the feasibility of the timing of arrival, factoring in considerable travel times. Chances are in most cases, people cannot join a scene in progress in a feasible amount of IC RP time.
