The proposed merger between Vodafone's UK arm and Three UK would, if permitted, represent the biggest shake up in the UK's mobile telephony sector in more than a decade. It would take the number of UK mobile players down from four to three. Nothing like that has happened since T-Mobile and Orange combined their UK operations in 2010 to form EE, now owned by BT, which took the market down from five to four players. The rationale behind the deal is that the UK mobile telephony market is just too competitive for the smaller players in it – Vodafone has…