I figured out that with a reset do defaults the problem remains ...
I will try to explain in details what is shappening so .. when a call is made the phone starts to allocate memory (ram) and it allocates it until the memory becomes 0 bytes and after that the phone restarts. This occurs only when a call is in progress when there is no active call the memory remains stable but when the next call occures it countinues to drain the memory until the phone reset