Especially if your service doesn't involve mailing me anything, and I live in an English-speaking country anyway. You don't have to do anything special for me; just let me in!

...just don't use ZIP codes for anything. That's braindead in this day and age, even if you do live in the US. Give the user Google Maps and a pin to drop—this lets people actually be exact with their location if they want to be, without giving you an address that could be used for spam mail.