Iphone6S: Contracts vs Leasing

I have always been on prepaid as I just moved from Canada to USA. However, I wanted to get the new iphone which would require me to sign up for a postpaid plan. I am still confused about the iphone6s pricing (as Canada never had the idea of leasing) even though I've been through several threads.

I was originally looking into AT&T and was going to do the 2 year contract for the 64gb iphone6s - the price would have been 299 upfront and I am locked into the plan for 2 years. However, irrespective of the plan cost, they still are charging me a device charge of 40 dollars?!

This brings to my next question , with the leasing or the NEXT program, the device charge is less but there is an additional leasing charge of 27/month. Am I correct to assume that this type of pricing will be identical across all carriers? I read in another thread that in the end, all options almost equal to the same amount. In that case, what would be the most cost effective way to get an iphone6s? (I know Traget was offering giftcards if you get a plan through the store)

Finally, my company actually will pay for the plan cost, but not the device cost - how does this show up on the bill?

Thanks in advance!