Can a GSM prepaid SIM card be purchased and activated in the USA for use in Germany or can they only be acquired there? IF they can be purchase in the USA, any recommendations as to what vendor to use or link to a vendor in Amazon?The phone is already unlocked.
Just as "technical heads up": GSM is 2G. Today you will get only 3G (UMTS) or 4G (LTE) tariffs. Berlin already runs test versions of 5G but not available to public. if your device do not support LTE it automatically gets a 3G connection.
Be aware which physical mobile network(s) can be used in Germany. Deutsche Telekom (T-Mobile) has a very high quality (coverage and speed), Vodafone a high one (data wise) and O2 is average. If you are traveling outside cities I rcommend the first two networks.
Also as info: in Germany you will find a lot of free wifi (correctly named WLAN). Ask yourself if you really need a SIM card.
I also replied to your other thread, but I will answer here as well:
If you do really want to have something before you leave (which is what we did last year), the Orange Holiday SIM worked flawlessly for us. There are two versions, both sold on Amazon.
Orange Holiday Zen with 3 GB data / 30 minutes calling / 200 texts
Orange Holiday Europe with 20 GB data / 120 minutes calling / 1000 texts
Thanks for the great responses.