Cingular - liquidated damages

I recently renewed my cingular plan via Amazon. I basically did this to get the Sony Ericsson W810i phone free. However when I checked my bill this month apart from the upgrade fees, I was charged an additional $30 as the "Liquidated Damages" charges. I called up the Cingular representative and asked her about it. She said that it was mistake on their part because I upgraded the plan via Amazon. However she did agree to credit the money back to my account. I would have definitely lost those $30 if I wouldn't have checked my bill in detail. I now just want to spread the word around so that people are aware of this problem.