Calls fail on 3G but fine on GSM?

[gadgetluva]

Has anyone else been experiencing a lot of failed calls on 3G but if you turn it off it works fine on GSM? AT&T really must be getting slammed with network traffic with this new iPhone 3G...

I'm in the city of Chicago, in the Lakeview neighborhood if anyone is in Chicago. I seem to get calls just fine though...