Hi FvM and thanks for your reply,
I understand that the Sim holder is very coupled with the Antenna, so for this reason I put an oscilloscope probe on the Sim card signal pad, in order to see the waveforms quality in the stress condition ... I noticed that the signals rising and folling edge are quite noise-less, the second order effect are small, so no overvoltage are present... nevertheless, the error message CPIN: NOT READY continue to appear after a while when the GSM signal strenght go down.
But my big question, which answer I haven't found up till now, is: What does it means CPI: NOT READY? which is/are the cause/causes? The Simcom AT command document doesn't give an explicit definition of it.
Many thanks,
Francesco