Setting up a location-based reminder on the iPhone is fairly simple. Those lucky souls with an iPhone 4S can just ask Siri to do it for them, but – like the rest of us – they still need to have an address in a Contact entry on their iPhone to make it work properly. Aside from typing in address information into the Contacts app, there’s an even easier workaround, using the Maps app.
Set Up A Location-Based Reminder With Maps [iOS Tips]