If you need an SSH client for BlackBerry, you can use MidpSSH. However, this client doesn’t allow you to use your BIS subscription. Luckily someone has modified MidpSSH to work over BIS.
Once you have installed the modified MidpSSH, there is a very good chance that your mobile operator blocks outgoing TCP port 22 on your BIS plan. You need to reconfigure your SSH server to listen on another port (port 2222 works for me).
In case you wonder how to specify the custom port (since there is no specific port field), specify the port in the Host field, e.g. 127.0.0.1:2222.
Hope this helps!