Originally Posted by androidfonefan
Only the ST Nokia smartphones have unlocked sims that can be transferred to other AT&T phones.
If you have one of those Nokia smartphones you can run the sim on any locked AT&T phone, you do not need to get a unlocked unit.
I think maybe I misunderstood your question. If you are asking if you can use the Nokia sim in a prepaid AT&T phone the answer is yes. I use my E71 sim in a LG Thrive which is one of their prepaid phones, my phone is not unlocked and it works just fine.
If you want to use your Nokia sim in a TMobile phone, that phone will have to be unlocked, AT&T sims will not work in TMobile phones otherwise.
Your info is actually outdated. You can now buy a sim card and put it into an att locked, T-Mobile locked, or normally unlocked phone. Also, if you do choose the unlocked sim, ST should choose the sim with the best coverage in your zip. So technically there are only two Sims.