Thanks for your detailed description.
I was just thinking that it might be feasible to build a i2c-iso7816 interface from the scratch, e.g. by utilizing a TDA8029 microprocessor as described here:
http://www.nxp.com/documents/applica...te/AN10207.pdf or http://www.bdtic.com/DownLoad/ST/AN2284.pdf

As far as I undestand the specifications (e.g. http://www.nxp.com/products/identifi...TDA8029HL.html) this could also work with 3,3V as supplied by jolla.

Interfacing from i2c to serial and then from serial to Iso7816 is maybe one step to much.
However, I have no clue how to obtain such a microprocessor, nor how to put the parts together nor how to write the code for both the microprocessor or the linux driver...
So, as long as no one else steps in and helps out with hard- and/or software design I guess it is the easiest (for me) to wait until you have your RS232-adaptor ready and I can play around with a serial reader and a 5V converter.
Thanks anyways!