If you are staying more than two years, it will probably make sense to get a long-term contract with one of the major German carriers. Usually, when buying a 24 months plan, the monthly payments will be less and you are able to get a phone together with the plan for a cheaper price. However, the downfall is that you are bound to that specific carrier and cannot leave the contract for 24 months. Therefore, the prepaid cards are always a good alternative.