I suggest reading the link that was provided and see if you have any questions.
Mine to you would be?
- Have you traveled before and used a Foreign SIM in your current phone? If not, then are you certain your phone is unlocked?
- Who is your current carrier? You may need to discuss with them your travel, what plans are available through them, if none or too expensive, then if you are able to install a different SIM.
For example, if you have ATT, you cannot install a different SIM while on contract easily, you would need an unlocked phone. Verizon does allow you to install other SIMs, but there is a procedure or settings that may need to be changed. T-Mobile allows use in Europe, as does Google Fi.
If all looks good for a SIM, then I suggest going with Vodaphone. Have the address of a store in Munich (there is a big one along the main drag) go in, they will help with the best option, install it, and verify that it is working. This has worked for me, but there are some reports that some stores are stricter about National anti-terrorism measures that require a permanent address (my hotel was fine in my instance).