Activate unsubsidized iPhone 5 - can I later switch carriers?

An authorized unlocked iPhone does not need a SIM card to activate the OS after a restore and it will work once you run through Apple's software setup screens when it asks things like if you want to set up iCloud or location services... Activation is just the process of checking whether the device should be carrier locked by querying a server of Apple's choice over WiFi and then updating the appropriate carrier settings if the ones loaded from the factory are out of date for a particular SIM or region.

Even in the US - iPhone 5 that are sold "under contract" to Verizon are not actually SIM locked and you can use them with any compatible nano SIM that supports at least one frequency and protocol that the phone model supports. It also is a A1429 model.

You can remove any SIM and power it on if you are worried about some carrier settings being locked.