If you unlock a T-mobile Sidekick phone, you can definitely use it with a Germany network's SIM card. To unlock a T-mobile Sidekick, you need to enter its unique unlock code. You can get the unique unlock code for a T- mobile Sidekick either from T-mobile network provider or from any trusted vendor online. Once you have received the unlock code, you can visit MobileUnlockGuide.com to get the free unlocking guide. Good luck.