Well yeah it takes a little longer because drivers aren't going to hang out in that neighborhood. You do eventually get picked up though. My experience in Baltimore with taxis is that no amount of calling will get them to come to a part of town they don't like. Nothing is going to change the fact that it is a crappy part of town but the difference between no pick-up ever and pick-up with a small glitch is huge for a lot of people living around those areas.