As eckhard mentions it is normally automatically displayed below 2500ft. Never flew either a 737 or A320 where that was not the case. The 737NG has at least two different display option in the PFD, either as a digital (between 2500 and 1000 ft) and round dial (below 1000 ft) in the upper right corner or as a digital readout in the bottom center of the attitude indication area. That said, on the 737 the baro altimeter has quite useful 500 and 1000 ft marks as well, although that could be a customer option.
