With Skype you can get a separate US-based number. So while you're overseas, people in the US can call or text it like any other US number and not have to worry about overseas rates. It's $30/year for unlimited calling out, $30/year for the phone number, and then pretty cheap for SMS. That way you get some whatever regular plan in Germany and then use Skype for keeping in touch with the US. With pretty much any smartphone you can use the native Skype app, or Fring, to access your Skype account over your data plan.