Well as far as i know the phone i once had was called an i9 with a sd slot underneath the battery. It was also dual sim equiped. It was the same thickness as the original iphone but the casing was removable. You have a great idea and please post pics of your progress!
the thing is that i dont know how to make one and how to do the software part. I just came up with the idea on the toilet and i was just wondering if it was possible to do and if some one want to do it you can because i would like to see it work for my itouch or iphone
Ideas come to you in all kind of places. Apple should have this feature for at least the micro sd then all you would need is an sd adapter but its a feature of many OTHER phones such as the HTC Touch with a micro sd card slot that you can have in any gb configuration. All I ever did was drag and drop music videos and movies to watch anytime on the Mobile 6 HTC touch and it was pretty cool and this was before the iphone entered my life.
Ureka-Apple probably would not do the SD card slot for one or two reasons the fact of dragging or dropping movies books and videos and playing them on the iphone simply bypassing itunes would be a big no no.