Why did Carlos Slim really resign from SBC Board?

Carlos Slim, the stealth telecom tycoon resigned from the board of SBC Communications, according to a 8-K filed with the SEC. Reuters reports that he has left for personal reasons. I take that with a grain of salt. Given his holdings in MCI, Global Crossing and scores of other telecom companies might be the real reason he left. Did the SBC board worry about the conflict of interest? I mean if MCI is competing with SBC, well he could be privy to a lot of insider information. Forbes magazine estimates that Mexican tycoon is worth $13.9 billion,