A customer has asked me to conduct a pen-test on the phones of their employees. The customer's target are the text messages within their employees phones. The text messages are stored on the SIM for security reasons. Physical access to the phones is allowed only when the phone is turned off. The customer has asked for what approach we're going to take on conducting the pen-test.
I came up with the following approach but it is not satisfactory.
Such as breaking the pin-code which is asked when the phone is turned on by cloning the card 1000 times and brute-forcing the pin-code. The idea is that if after 3 tries the first card locks. I then continue doing the same with the second card. This way I have more chances for brute-forcing the pin.
First question: Is this a good idea or are there any flaws in this approach?
Second question: Can you advise me on a better/easier/cheaper approach?