Since Amazon sells the GS3 for upgrade customers like myself for $149, that's a $50 discount from ATT. On top of that Amazon does not charge CA sales tax which amounts to another $50+ discount, nor do they charge restocking if you decide against it in the 30 day trial period. So there's total savings of $100. Of course if you're a new ATT customer you'll pay $189 instead and if you cancel the contract after the 30 days you'll get slapped with an ETF from both Amazon and ATT, so make sure you're going to stay with ATT.
Am going to assume Amazon will have the garnet red color once ATT has them and it will be sold for $149 also.