If you use the SIM cards SMS storage (on a GSM phone) it's not that trivial to obtain the PIN. However, it's very likely that your mobile provider is able to ga

If you use the SIM cards SMS storage (on a GSM phone) it's not that trivial to obtain the PIN. However, it's very likely that your mobile provider is able to gain access to the card (e.g., by using the PUK code to reset your PIN code). Other means would be to use an application such as TextSecure (for Android) that uses public key encryption to immediately enrypt all incoming SMS and that requires a password to unlock the private key needed to decrypt the SMS. In the long-term what I'm waiting for is some open-source Android fork that provides full-root encryption using LUKS. This should suffice in preventing others from reading your messages.