If you are on AT&T or T-Mobile, and have a quad band phone (most newer models), your phone will work in Germany provided you have enabled international roaming. This can be done online or by calling the service center. Both ATT and T-Mo use GSM networks which are in Germany. Verizon uses CDMA, but if you get a SIM card (available for some VZW phones) it will work there too. Be prepared to spend ~$1/minute for roaming.