Thanks for using the forums to get this issue with your mobile services looked into, I am sorry if this has been causing some frustration. I would be more than happy to look into this for you.
Can you tell me whether an error message appears on screen when you insert the SIM?
Also, what does the message state when you try to call someone?
Does it happen with all numbers or just particular ones?
Have you tried the SIM in another phone to see if it works?