Maps don't generally have the names of businesses on them, which is generally what I'm using it to find. Even if they do, its only businesses that existed when the map was printed, and I live in a place where these change frequently. Generally if I'm with a group and we'll walk all over the place to different locations in a given night. Having to pre-plan and research a list of places to go(only for people to change their minds), or carry an unwieldy map of a large area is pretty burdensome and would change our plans for the worse. Granted, it would be sufficient for one person to have such phone service, but being at point A and being able to know how to get to point C without stopping at home first seems pretty worthwhile to me.
Assuming you have home internet service independent of your cellphone, why not make "calls" over that? Voice phone service seems useful if you are travelling to remote places where, if you are seriously injured, no one would wander by to help you. Other than that it seems like a luxury compared to email + maps to me. I pay ~30/month (it varies based on use) and am going on 3 years with the same phone, not really all that bad considering.