If you will be moving to or staying in DL for more than 3 months ... (non-German citizens only!), then this is normally not a problem. You can apply for a permanent German Amateur Radio License with call sign. If you have a CEPT License, submit a copy of your HAREC certificate, your passport and your working and/or residence permit (EU-citizens: submit a copy of the registration form from the local Einwohnermeldeamt) to the BNetzA office in Dortmund. If you wish, you can state the call sign that you wish to have (if it's available!). List a few possible calls. If you have no CEPT license, please submit a copy of your passport, your working and residency permits, as well as a copy of your own Amateur Radio license (if possible submit an English or French translation of it, but for U.S. licenses a translation is not necessary) to the BNetzA office in Dortmund. In either case: do not hesitate to contact the office if you have further questions. They will give you the needed information:

Bundesnetzagentur (BNetzA)
Alter Hellweg 56
44379 Dortmund
Germany
Phone: +49 231 9955 - 260
E-Mail: Amateurfunk@bnetza.de

Application for a German Amateur Radio License

For more information, please look at the "Visitors to DL" page