I was going to say the same thing Barry, however I realised that more than just contacts can be saved on the SIM card, especially if it's an old SIM that was used in an old phone (back when phones used to utilise the storage in SIM cards, albeit a very small amount of storage).
The following information may be on the SIM: user identity, location and phone number, network authorisation data, personal security keys, contact lists and stored text messages.
That's why I didn't bother to respond to this question when it was first posted, because Togo has given very good answers :)