Analise, if you read through some of the threads I linked to you'll find some discussion of prepaid voice.

How long are you going to be in Germany and how much use of the phone do you want to do?

I'd recommend one of the discount cards, such as those sold at Aldi, Tchibo, or Lidl.

I wouldn't pay any attention to rates to the US. It will be cheaper to use a voip/calling card provider with a local German access number and call that from the cell.