So, board is done and soldered and attached to a phone. Sony-Ericsson Z530I in my case, you can find used one for as low as 5$. I've attached everything to a polystyrol plate, just for stiffness, plus added a hole for VGA camera to test it too.
Here you can see SIM card inserted in the phone and cell phone battery connections soldered to wires. These wires then connected to a battery (read more about this at the end :))
Here is a view of a cell phone connected to a soldered oshpark board. You can see all 11 MOSFETs (10 for manipulating buttons matrix and 1 for triggering power-on/off button).
Here is a video of how it PERFECTLY! works :) as a tes I sent a text with Hackaday in russian to my phone, but camera manipulations, GPRS/Edge browser works, everything.
And here is how it looks on the serial port as Atmega chip provides feedback about "pressing" buttons (array pos - position of requested key in a buttons array, then it tells you the corresponding input and output MOSFETs triggered, their local Input/Output number and their arduino PIN number)
P.S. I spent so much time trying to understand why my phones are just switch off immediately after powering them with the SIM card attached. Purchased same models, tried different batteries, etc. To find that the problem is with length of wires from battery connector to the battery :) looks like only 10cm is OK without extra soldering in between. Here is how my floor looked while I was trying to find the solution
Will publish files shortly.