Cannot connect due to sim-card problems Cannot connect due to sim-card problems

Trying to get started with my iPhone 4, which I recently bought from one of my mother's colleagues.

But when I get to the activation of the iPhone it shows a message on the display that says: "Only compatible SIM cards from a supported phone company may be used to activate iPhone. Insert the SIM card that came with your iPhone or visit a supported telephone company store to get a replacement SIM card ". This suggests that the iPhone is not unlocked for other phone companies, but the other day I was in a store and got the phone unlocked. Therefore I can now not figure out what the problem is. When I connect the iPhone to iTunes quickly a message appears on my Mac, which says: "The SIM card inserted in this iPhone does not appear to be supported", and then the same message which is displayed on the iPhone. Some geniuses who can help me?

Thanks,

Johan Helms