td5 stereo fault

Hello all, I have a fault with the landrover cd stereo on my 2003 disco td5, sometimes it works fine, radio and cd, but mostly it pwrs up and says 'PHONE' in the display with no other functions or sound working. I removed the unit unplugged the connectors and the the fuse on the back, then plugged them back in and re-did the code and it worked ok for about 3 mins then said PHONE again and froze all other funcs. so I removed it and re coded again and it worked ok!! Anyone got any ideas. Also if I want to fit an after market stereo, is there a kit available to connect up to the original connectors and still be able to use the steering wheel controls?