Yes and no. 3G SIM cards (also known as USIM) also work with GSM phones. But they are a significant improvement on the SIM cards that were available in the 1990s. In terms of security, they include a more powerful algorithm, based on the latest cryptology research.
They protect you from fraudulent access to your line, and thus from charges for calls you have not made appearing on your bill. In addition, new systems have been developed to prevent illegal eavesdropping on your communications. The SIM contacts book has a larger memory, allowing you to store thousands of entries and contacts with a larger number of fields (such as email addresses and secondary phone numbers).
The USIM or 3G SIM is also a mini-computer that allows different applications to run at the same time, providing a contactless card for the subway as well as an address book and portal to local services, for example. For more information, visit the GSMA website.