What chips does a Sony Ericsson (feature phone) use? (e.g. K510i, K610i, W705, C510)
There's a website called ifixit that does "teardowns" of phones that may be of interest to you; or you could do it yourself by dismantling a phone and looking at the chips. Here's an excellent example by Bunnie Huang.

You will face 3 major problems:


the radio software is far too large for one person to write (although some of the SDR-GSM people have got most of the way, and it's all specified in 3GPP).
you need approval from your local telecoms regulator to use the phone if you've built it yourself
many of the cheap chipsets used simply aren't sold to the public. You'll have to get yourself a good Mandarin interpreter and buy them under the counter at Shenzen. The documentation (if any) will also probably be in Mandarin.


Video and audio decoding will nearly always be hardware-accelerated. Storage is usually DRAM and Flash. Either separate or "chip-on-chip" like the Pi.