My data plan covers 100 MB, after that it is throttled to 64 kbit/s. SMSes are 20 ct each, calls are free to the same cell network and all landlines. But this is an add-on to my DSL/landline contract; the first SIM is free and the second one is just 2,99 €/month. So my wife and I can call each other for free, and the low data cap is an inconvenience for me, but not important enough to switch to a more expensive plan. I use the data mostly for games anyway, and WhatsApp works fine even with throttled data.