So you can call any number and have a converstion, and the phone works fine, but when you want to get what we call Voicemail (I think thats what you meant), then the phone freezes and turns off? Have you checked in the Settings or Phonebook what the voicemail number is compared to what your Service Provider says it should be? It is worth trying another SIM in the phone and calling Voicemail, just to see what happens.
