is T-Mobile cheating its contract customers?

Think about the following when you ever get a new t-mobile contract in Germany with a subsidized phone. It is SIM-locked. I discovered that today, when I was trying to exchange my SIM cards. A few weeks ago I subscribed to a 24 month T-Mobile contract with a flatrate and son. The contract seemed to be the cheapest for me. When I was in the store I thought about a new mobile phone, in addition to my Nokia 3230, which I am using in daily life because of the open OS. So I wanted to use the new one, a Samsung Z400 for fun. I am not really happy with it and the functionality is not that good, I want to resell it or give to a good friend. My problem is now, that I was not told the fact of the SIMlock in advance nor is this written somewhere in the contract, any avertisment or any information flyer or brochure. I would have taken the contract probably anyway, but I would have not taken any phone. I understand that I am not getting a subsidized phone with any pre-paid contract or that I have to pay for the phone, but I really think, that I should be told the fact of the SIMlock in advance in the store or in the documents. Thanks to T-Mobile for fucking up my sunday evening. Lets see and wait what the complaint departement will tell me tomorrow. Oh, btw. they are not working on Sundays :-)