If you've got the account set up only in telepathy, then you can initiate a chat by opening Messaging, tapping the speech bubble icon in the bottom right corner, then selecting a contact from the list.

I've attached provider and service files for gadu-gadu. Copy them into /usr/share/accounts/(providers or services), delete your old mc-tool account and register a new one with the Accounts app. There are no gadu-gadu icons in harmattan - you'll have to make some

Let me know if it works, I don't have a gadu-gadu account to test with.