The solution is to change the phone settings band option from auto 3G/2G to either 3G Only (WCDMA + UTMS 2100 in Europe) or 2G Only (GSM + AUTO) depending on your requirements.
Also read this thread new SIM solves problem where the resolution was to get a new SIM.
Obviously this only solves the problem when the crash is because of the sim and/or settings which impact the sim. To rule out a software cause its best to start with a hard reset.
Edited by Nick Le Lievre, 31 July 2009 - 01:41 PM.