Hi,
Unfortunately you're out of luck there as non 3G phones (such as the BB7290) apparently won't take USIM's. At least that's the official story; you can still try it out
Should this work then you will only have simple mobile phone functions anyway as you would need to sign up for a BB plan for the complete BB experience.
Bear in mind that by forcing the phone to constantly roam you won't abide to Three's "Terms & Conditions" but apparently they very rarely enforce them.