British Telecom was having a better time, with conditional or 'grey' trading by institutional investors in its soon-to-be demerged mobile phone arm mmO2 beginning today. Shares in the new firm jumped from 68p to 75p, valuing the arm at around £6.5bn, while the remaining core BT business slipped slightly to 252p in the grey market. BT rose 1/2p to 325 1/2p.