What you are using is not a USSD code, but rather a service code (for call diversion, in your case). They may look the same, but they are, in fact, not.

USSD is indeed implemented now in PR1.2. "Classic" service codes seemingly are not.

Goes to show you that obviously there is no seasoned developer and no seasoned product manager with a decent telephony background in the entire N900 development chain.

But then again, of course, let's all repeat the maemo.org mantra: the N900 is not a phone!

Regards,
Chris.