It seems the Cingular users have discovered that Gemplus 64K SIMs cause very odd (bad) behavior in the 650.

I'm on T-Mobile and some of the symptoms they describe (slowdowns in Phone, etc.) have been happening to me as well.

So, I popped the T-Mobile SIM outta my 650 and I noticed a curious little logo on the backside (non-contact) of the SIM: it looks like a G with a + in the middle -- is this Gemplus?

If so, has anyone identified that this could be causing problems with us T-Mobile 650 users as well?