SIM for Germany and Czech
 

May I know that what SIM card will be used for both countries? If not, I need to buy two different SIMs for Germany and Czech?

I have read Fonic SIM package from a blog, it costed about EUR 9.x for 500MB/month. It's seem a good and cheaper option. However, the activation seems a bit complicated. And, can I buy it in supermarket?

Will there any other SIM is better than Fonic? Will Fonic can also be used in Czech? Thanks for your help.

Fonic is a good choice though Lidl mobile, which comes from the same company but is only marketed through Lidl supermarkets, is cheaper.
You'll find detailed info about Fonic and Lidl on the numerous threads on this forum and at
Germany - Fonic - Prepaid Wireless Internet Access
LIDL mobile - Prepaid Wireless Internet Access

Thanks for your reply. May I know that Fonic is just for Germany only?

If you activate the 500MB data option (so-called "Handy-Internet-Flatrate") which costs € 9.99 for Fonic or € 6.95 for Lidl data roaming in the EU will cost € 3 per calendar day but you will only have 10MB per day after which the connection will be interrupted.
With all other data options (even including the larger 5GB data option offered by Lidl) Internet access in the EU will be billed with € 0.83/MB (billed in 1KB increments).

Thanks for your information. I am much more clear now.