There were a couple of international sellers of Fonic SIM cards who ship worldwide but please notice that, as described here, after registration Fonic will send out a confirmation letter to the provided registration address and if this letter cannot be delivered your SIM will be blocked. So in addition to buying the SIM card you also need to make sure the confirmation letter will be delivered to some German address, be it a hotel or a German resident who would temporarily put your name on his mailbox.

Thanks for your information. Maybe purchasing the Fonic Sim at Germany is a better option. I have searched some markets in Munich, like dm, Lidl, MediaMarkt... The locations of dm seems easiler to be found. Will there any other shop or markets near the Munich Hbf? Thanks a lot

There is a Saturn store 10 minutes walk from Munich Hbf, at Neuhauser Straße 39.

From Munich main station the best option would be to go to a Lidl supermarket and to buy a Lidl mobile SIM, which actually is a second brand of Fonic and most importantly is a bit cheaper than Fonic.
For more information on Lidl mobile read LIDL mobile - Prepaid Wireless Internet Access

There are two Lidl supermarkets close to Munich main station:

• Lidl at Schwanthaler Str. 31, 80336 München (350m, 5 min walk)
  It's at the site of where Google Street View shows the now closed "müncher electrowelt": Google Street View
  
  
• Lidl in the Central Bus Station (ZOB - Zentraler Omnibusbahnhof) Hackerbrücke 4, 80335 München (700m, 9 min walk)

Both are opened daily except for Sunday until 20h.

Thanks again.

Those links are very informative and give me a great help. Many thanks.

Fonic cards for sale over in sales...
 

If anyone is interested - excuse the intrusion... :)

Fonic Update?
 

Does anyone know if Fonic still (as of April, 2013) sends a letter to your Germany address to verify residency? Can I have the letter sent to a hotel I am staying in?

Thanks!

Yes, they do.
Yes, though you cannot add your hotel's name to your shipping address. But postmen should usually assume that you are a guest if he can't find your name under the given address and thus drop it at the reception.

So after searching a little on the forum I decided to get a Fonic sim card to use in Germany for a couple of months.

After one week they locked my sim even though the address of the hotel was correct on their site.

I found their official facebook channel and it appeared a good option to use since there's a lot of non german persons complaining there. But even after confirming the correct address they still did not unlock my sim.

Do you guys have any sugestion on how to proceed? Have anyone gone through this?

I understand some Fonic users have emailed Fonic and given them a different German address. Fonic sent out the confirming letter again, it didn't get returned to them, and their SIM got unlocked.

I am curious - did the address you gave Fonic include the hotel name? Apparently it should NOT. So, for example, if you are staying at the Hilton in Ramstein and the hotel address is Hilton Ramstein, 24 Main Street, Ramstein Germany 45555, you would give Fonic the address as Your Name, 24 Main Street, Ramstein Germany 45555. You would also need to tell the front desk what you are doing and hope the postman will deliver the mail to you at the hotel.