If I wanted to carry a calculator...

...I'd carry one. And probably buy a pocket protector too. But I don't, and my phone has a calculator built in anyway.

My employer already foists a second phone, two smart cards and two RSA tokens on me, none of which I particularly want to carry, but I do because it's part of the job. If a supplier (which is all a bank really is) wants me to carry more crap around, they can stick it.