I sure wish you could buy a DSLR that just plugs into your iPhone. I don't want any of that terrible DSLR software -- just the hardware.
I think many devices should become BYOD (bring your own device) soon, including big things like cars.
edit: I don't just want my pictures to be saved on my phone. I'd like the phone to have full control of the camera's features -- so I can use apps (like timelapse, hdr, etc.) directly within the camera.
None of these solutions are perfect, but just fyi:
1) Samsung has released the Galaxy NX: a mirrorless interchangeable lens camera, which has a DSLR-sized APS-C sensor, but no actual mirror. The back is essentially just a big Android phone.
2) Sony sells the QX-10 and QX-100, which are just the lens, and you wirelessly connect them to your phone. The QX-100 has the same 1" sensor as the best pocket camera you can currently buy (the RX100).
3) Both Sony and Canon make wireless cameras (Canon 6D [full-frame], Sony RX100 MII [1" sensor] or A7/A7R [full-frame], maybe others), that let you connect to a phone or tablet and view a live feed of what the camera sees, change the aperture or other settings, trigger the shutter, and receive photos on your device. I'm unclear how open the Canon API is, but Sony has their own ecosystem of interesting apps (http://playmemoriesonline.com/) that let you do things like set-up time lapses. The Sony UI is pretty clunkly though, I would greatly prefer an open API.
I'm interested why you'd want DSLR, though, because if it attaches to my phone i'd probably be happy to use the phone screen as the viewfinder and save the depth and weight that would otherwise go to a moving mirror assembly.
I recently got a Canon 6D. It has built-in wireless which allows you to connect directly to your smartphone so you can download photos from the camera to your phone. It works really well. You can also use your phone as a remote control to take photos and the view finder can be seen on your phone. I love that camera.
I believe the Canon 70D does this too (which is not a full frame like the 6D, but a APS-C cropped frame), as well as some of the Panasonic m4/3 (micro-four-thirds) cameras like the GH3/GH4 and GX7.
Creates a hotspot that your iPhone can connect to. Photos are then immeidately moved to your device as they are saved to the SD card by the camera.
I havent tried it, but Ive heard it works well for quickly sharing pictures. Downsides are cost compared to normal SD cards and battery use by your device.
I have tried it. In the default configuration, it tries to upload all photos online whenever it finds itself in the known WiFi network. I didn't like this.
Direct transfer to other devices is possible, but the configuration UI is horrible. I spent half a day to configure it. Did I tell it doesn't work in Linux? Bottom line: I managed to be able to browse the contents of the card from the Windows PC, and much slower than if I inserted it in the card reader.
On the go, EyeFi is almost useless. The best configuration that worked for me (without synchronizing everything, but uploading only selected shots and only to the phone) was with phone providing a WiFi hotspot. And it eats the battery pretty fast. WiFi connection attempts take forever. I had to prevent the camera from sleeping too. Transfering huge DSLR files to the phone was always an overkill.
On the scale of 1 to 10, I'd give EyeFi usability a solid 3. It kind of works, but it didn't solve my problem.
Worst of all, some files were not saved properly (they remained 0 bytes). It happened at random, but regularly. Afterall, I retired the EyeFi card and switched back to normal SD cards which are faster and much more reliable.
But the scenario you seem to lust for (a combination of high quality DSLR hardware and a competitive app market) will never manifest because the hardware is too fragmented. There never will be standard interfaces, and you won't get enough competition to develop the greatest possible camera app for a specific hardware model.
I think many devices should become BYOD (bring your own device) soon, including big things like cars.
edit: I don't just want my pictures to be saved on my phone. I'd like the phone to have full control of the camera's features -- so I can use apps (like timelapse, hdr, etc.) directly within the camera.