I belive the Skype for 3 UK will be the same as skype on all the other 3 phone.
Id est a customized version of iSkoot client for skype (iSkoot | Life on the go.
). Iskoot is available for blackberry.
The particularity of 3 customization, beyond the graphics, is that iskoot will call their local access point, and no iskoot ones, with no mobile phone call charge for that (read about iskoot way of working) since the gsm call will travel on their own network.