pau1j is correct, you can just log into any BT Openzone hotspots using your My Account username and password. If you're still unable to login, please try this link, click on 'business customers' and then 'Activate your WiFi'. I'm confident you'll then be able to hop onto the hotspots.
I think the App you're referring to is 'My Vodafone' which was made available to BlackBerry customers earlier this year. Just search for it on the BlackBerry App World and you'll be able to download it.