Buying an iPhone 6s without a contract

I'm a travel photographer. I currently use my iPod touch as my travel camera. I connect via wifi to post my pics and to connect with the cloud. It works fine for me, but I'd like a better camera. I want to buy the new iPhone 6S Plus unlocked and without a phone contract. I intend to use it as my main travel camera. Can I buy one without signing up to a phone carrier? I just want to buy one and be able to turn it on and use it, much like I use my ipod touch. I want to be able to use wifi to access the net, and when I travel abroad, I want to be able to pop in a temporary sim...but don't want to get locked into any plan from the carrier companies.

is this possible? Can I buy an iPhone 6S Plus, open the box, access my wifi at home and activate my iPhone without a carrier - like I did with my iPod touch?

i already have an unlimited data plan for my iPad from ATT that I am grandfathered in on. I don't want or need another monthly contract from a carrier. ***Speaking of my iPad data plan, could I swap my micro sim from my iPad to the iPhone 6S plus to use data on it? Just curious.

I'm also interested in the new Apple monthly plan where you can update to a new phone every year. Can I do that without also buying a phone plan from a carrier.

Again, I'm just interested in the iphone as a travel camera. I can already make calls & txt on my iPad & ipod touch. So I just want to be able to buy the iPhone 6S unlocked, turn it on, activate it via wifi and GO! :-)

thanks