If you keep the nokia cover and integrate it with the leather case I don't se any use for the leather case...
The idea of a case is to protect the screen and offer a means of attaching it to your belt. And yes probably store a mmc, but how often do you really change the mmc card?
The nokia cover already gives great protection when keppt in a bag.
The incentive for me to buy a new cover decreases, when the only new thing in terms of functionality would be a beltclip... and the added bulk alone probably would put me of. Without any cover the device is 14 mm thick, thats ok in my book. With the nokia cover that goes up to 19 mm thats the limit for me... By adding i guess two layers of leather ontop of that i guess we end upp at about 23 mm. Thats almost 10 mm extra bulk .
So please drop the idea of integrating the nokia cover in the case

I would like to se a leather case that is slim, gives me the posibility to use all the connectors when in the leather case, also when the screen is exposed all the buttons and the stylus should be available.

The cover could be made of a durable plastic conseald in the leather covering the screen. Together with this plastic inside the leather there could be added a small magnetic strip that when folded over the screen puts the device in sleep mode.

And the beltclip should be kept simple no fancy plastic thing that breaks or takes up to much room when not clipped to the belt. One should be able to place the device on a table without it wobbeling around.