I'm really hooked on my 600, but it sometimes performs like there's no signal even though I'm showing max bars. It's an AT&T Wireless phone that is now on the Cingular network. I'm running software version 1.1.3 but have downloaded 1.1.7. Any hope this will solve my problem. I'm giving it one more day and then it's off to the Cingular store for a 650. My office mate uses a 650 and his works great (even in the elevator). I can't conduct a decent conversation even while sitting here in the office.