This solution holds for Nokia 6700 slide with insert sim card problem. Just refer to the solution below if the device is unable to detect any kind of sim card being inserted to it and it shows "INSERT SIM CARD" or Sim Card Not Inserted".
Nokia 6700 slide SIM card ways
You may first try to clean the SIM card pin connectors and its surrounding components and ensure that it is free from oxidation. Check the VSIM and GROUND pins connection line paths, the rest pins is connected directly to the GAZOO chip.