Download these smart-phone applications for urban travel.

Exit Strategy NYC ($4.99) Maps of New York City’s MTA transportation system, plus the most convenient exits for your destination.

HearPlanet ($4.99) Supplies Wikipedia-powered audio commentary for buildings and other landmarks near you.

Postman ($0.99) Create and send virtual postcards using your (or your kids’) photos.

SitOrSquat (free) Find a restroom or public toilet almost anywhere in the world.

Taxi Magic (free) Book taxis and town cars directly from your phone.

TeleNav ($9.99 per month) Turns your device into a GPS navigator and ATM locator, among other things.