How involved do you want to get ? I just replaced the stock am/fm/cass with a JVC KB BT-1 am/fm/cd/usb bluetooth head unit and 4 pioneer speakers in the stock location. I got the head unit from www.crutchfield.com
, came complete with wiring harness to plug into the stock harness, face plate adapter and good instructions on the harness, $279 shipped. The speakers I bought last year and they came with speaker wire adapters. Works for me and I use my cellphone alot.
I have a very similar system in my 98XJ only the head unit is a jensen.