British Telecommunications Plc has not yet finished turning the world telecommunications market on its ear. It had been assumed that Telefonica de Espana SA would team up with a US phone company to pursue its ambitions to conquer Latin America, with GTE Corp high on most lists but now it appears that the Concert alliance is becoming so attractive that all those that are not effectively barred from joining Concert are prepared to tear up all their existing alliances to get on board what is becoming the runaway market leader. According to Reuter, an announcement may be made as soon as this week, and Telefonica shares advanced in Madrid yesterday in anticipation. An alliance with Telefonica International SA, in which the Spanish state still holds 20%, would deliver a dominant presence in Peru, Argentina, Chile, Venezuela, Colombia and Puerto Rico, but some observers question whether Telefonica would be prepared to go so far as to cede a stake in Telefonica International, especially as it is seeking to buy the Spanish state stake. Even so, prising Telefonica away from the Unisource NV alliance of Telia AB, Koninklijke PTT Nederland NV and Swiss PTT would rank as a major coup. British Telecom is already close to landing Portugal Telecom SA, with its strong Brazilian links via its partnership with Telebras, for Concert. And MCI Communications Corp delivers access to Mexico via its Avantel SA joint venture.