I finally got it working. I tried flying from KSFO to KOAK, and submitted my flight plan through sb747 itself. The controller talked to me very briefly in the beginning but didn't continue afterwards (but then again, I only had text available so if he said something, I couldn't hear him). VATSpy showed me but with some minutes of delay.
It was not an excellent flight (
link) specially for take off, because of the massive crosswind (270@20G24) and I didn't actually follow any procedures (neither joined the pattern nor used an instrument to land). I was totally side tracked by trying to connect to the controller. But still, it was a good start.
What I need to learn now is how to run the Advanced Voice Controller to be able to establish voice comms with controllers (I need to know the server and room information, where to find them, and the keypress assigned to switching mic on and off).