Can i use a data plan on a unlocked phone?

Well, recently i bought the Xperia X10 Mini Pro, and its a ty phone, so when i bought it, it was fatory unlocked, and it was kinda pricy, so when i went to my carrier to buy a data plan, they "activated" the plan, but the internet never worked, so they told me it wasnt their fault, it was my phone... So i was wondering if i can use a data plan on a factory unlocked phone, cause m thinking to sell it, and buying a old 9790...
Thanks anyway...:D:D:D:D

You probably need to input your carrier's APN settings for the internet to work for the Xperia as it is an Android device.

For an unlocked 9790, you will need a blackberry data plan that has BIS codes on it.