Iphone - buying an iphone offline from Apple and buying a sim only?

Does it not work out cheaper, to buy the handset offline, and have a sim only contact and buy a nano chip separately?
if you buy it from the apple store do you have to pay vat?

what is the cache?

It should work out the same. Buying offline or online is the same price, and likely for the SIM as well.

Also its what is the catch not cache.