Which SIM cards are needed?

Standard USIM in mini-SIM format, see http://en.wikipedia.org/wiki/Subscriber_identity_module. When concluding your contract, please insist that the maximum speed supports HSPA+ or higher, and can thus offer a download speed of more than 7.2 Mbit/s.

Does it make sense to use SIM cards from different providers?

Yes, we recommend this expressly at least for Germany. The reason for this lies in the history of private mobile wireless. In the early days, the regulatory authority for telecommunications and postal services prohibited D1-Telekom and D2-Mannesmann from sharing the use of radio masts. That is why the networks still do not cover exactly the same areas and the best reception is only possible with both networks.

How can I avoid high roaming costs abroad?

Simply purchase prepaid services of the transit country for when you are abroad. That is easier to do than before and much, much cheaper. We will be happy to notify you of the necessary settings. The works settings of the CAR-A-WAN do not permit "roaming", so the modem only goes online if it thinks it is not abroad ...