My SIM card also behaved badly in other phones. So I called Cingular and for a not-so-small fee they're sending me a replacement SIM. Once I get it tomorrow I should be back in business.
I've decided the SIM had a mechanical failure of some sort, or perhaps a physically induced data scrambling. The intermittent behavior I experienced was indicative of that. For instance, when I called 611 from the phone for service, sometimes the automated attendant knew my phone number, other times it asked for it as it would if I was calling from another phone. My phone would show a full strength signal and then disconnect when I tried to make a call. The wife's SIM in my phone worked perfectly, BTW.
Looking forward to having a reliable phone again.
