It depends on the situation.

If the Verizon phone is outside with clear lock on GPS satellites, then
it's likely to give an accurate location to within 50 meters or so most
of the time, and 150 meters nearly all of the time.  Cingular's
implementation (TDOA) has an accuracy in the same ideal conditions of
about 100 meters, most of the time, and 300 meters almost all of the time.

If, however, the Verizon phone is inside of a building or otherwise is
prevented from getting ag ood GPS lock on its own, then it must use
local cell sites for position triangulation.  UNder these conditions,
it's about equal in accuracy to the Cingular phone.

When you get down to it though, 100-300 meters considerably narrows down
your position and in many cases, should be good enough.