You say you have a iPhone. What kind?
If it is a 5, it is no problem.
I have a 5 myself, and no simcard, and the google maps app and even the iPhone map will provide your current location at any time.
It is really convenient, as the small blue dot move as you move.
Even if you are online (wifi) and type in an address and start the GPS directions it will continue even though you are offline.
I say it is worth the upgrade, if that's the case.
I've been traveling for 7 months, around the world, never used a SIM card anywhere.
Good luck