The prepaid SIM is basically free, as the SIM’s price of 10 Euro is already included as balance. Traffic used by WhatsApp is not counted against the included data volume. The SIM card can be ordered in Germany, starting today. via Link
If you are travelling in Germany, you may like to consider in getting a WhatsApp SIM powered by German carrier E-Plus. The WhatsApp SIM is priced at 10 Euro. All the data traffic caused by WhatsApp does not count against that data limit, however calling and SMSs might be a little expensive.
A minute of calling or a textmessage sets you back 0,09 Euros, an MB of data costs hefty 0,24 Euros, unless you order an additional option called WhatsAll. With WhatsAll you can call, write texts or use mobile data with an amount of 600 flexible Einheiten (units) for 10 Euro in 30 days. 1 Einheit is either an SMS, a call of 1 minute or 1 MB of mobile data.
I wonder when will WhatsApp launched its Sim card in Singapore. We have something of similar by Singtel thou. A user on the Singtel WhatsApp Plans pays S$6 a month for unlimited usage of Whatsapp and does not count into the data volume too.