Shares in Vodafone VOD.Lfell as much as 1.7% and Telefonica TEF.MC, which owns British telecom services provider O2 UK, was down 5.5%, as its shares traded ex dividend in Madrid. Adds BT comment, detail, updates prices Dec 12 (Reuters) - BT Group BT.L shares fell more than 4% on Tuesday after Britain's telecom regulator proposed a ban on inflation-linked price rises in the middle of customers’ mobile and broadband contracts. BT noted Ofcom's consultation into inflation-linked pricing mechanisms and said it had always followed their guidance.