I've a employees contract from T-Mobile. That's basically a Combi Flat M with mobile-phone but for 19,95€ per month (instead of 59,95€ per month). That's Data-Flat, Festnetz-Flat, D1-Netz-Flat (Calls/SMS/MMS), T-Mobile-Hotspot-Flat.
0,203€ per call to other networks (0,29€ - 30% Rebate) and 0,133€ per SMS to other networks (0,19€ - 30% Rebate).
So if you know someone who works at T-Mobile you can ask him to get that contract for you.