Mutiple SIM cards are not working in my purchased un-locked iphone and ipad.??

I travel a lot around the world and previously was able to insert a sim card from another network into my iphone and ipad and it worked perfectly.

Recently I updated my iphone and ipad to iSO 6.0. and after that when I put my German SIM card in to both iphone and ipad it would not work any longer?? Got a message No service and after Invalid SIM

I double check with my Carrier and was told all my SIM cards are fine and working correctly from their end.

I then put the sim cards into another HTC phone and it worked so why all of a sudden my iphone which I paid alot of money for purchasing a UNLOCKED phone as opposed to being strapped down with a 2 years contract now my iphone doesnt work with using different sim cards??

Please HELP?