[Motel75]

All German mobiles cost about $2 per minute to call the US. If you want to place lots of international calls, get an international calling card or go to a calling center (a private company offering cheap phone calls from its own store; you'll find these in big cities or near stations).

There are plenty of SIMs available, so that should be no problem. Sometimes they are even cheaper with a phone (though the discounters such as Aldi never offer cheap phones).

Contrary to the above, Vodafone is not a bad choice if you plan to call occasionally and mostly just want to be reachable. The main operators' SIMs have similar (high) prices, but relatively long validity, so if you're coming back each year you might want to consider this (however, if you get Aldi Talk, and then add 15 euros to it, the account will be valid for 2 years). For the US, T-Mobile might be worth considering, because the company is present in both markets (though they offer little in the way of service for non-US customers).

The best offers with a phone can be sometimes found in department stores such as Karstadt or Kaufhof and electronics retailers such as Saturn and MediaMarkt.

Failing that, Vodafone has a special on during the World Cup at its official stores: a Motorola phone plus SIM for 33 euros with 5 EUR credit. You can often get this for less at the retailers mentioned above, but it might be a good fallback option. But you should be able to get a SIM for 10-20 EUR or one with a phone (sometimes even a triband model) for 20-30.