There are some great iOS (iPhone/iPad) and Android GoToMeeting clients, but so far Blackberry isn’t supported on the whole. Blackberry Playbook support is something that Citrix are looking at. Citrix have already built Citrix Receiver for the Playbook, so hopefully a GoToMeeting blackberry app will be forthcoming. You might be able to get gotomeeting to work through a java or browser client on a blackberry.
If you desperately need blackberry support, Fuze or WebEx may be worth a look.