help with internet connection

[Teabag Tim]

Hi, another new guy fishing for some help please. I have an unlocked i phone 3G, I have put my BT sim in it (initially in my Blackberry ).
All is well except when I try to connect to the internet out and about. I can get a connection on Wi Fi. My service package is unlimited internet for Blackberry. When I try to connect the message displayed is;'could not activate cellular data network: you are not subscribed to a cellular data service'. Any thoughts please

 

[Tramain]

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