In one of its most emphatic victories yet over its upstart rival, British Telecommunications Plc has bounced Mercury Communications Ltd payphones out of the UK Post Offices run by Post Office Counters. The Post Office snubbed British Telecom, for decades its Siamese twin, by signing Mercury to put pay phones in 200 Post Offices in 1989 (CI No 1,137). Under the new agreement, those will be replaced by British Telecom phones; the five-year agreement, terms of which were not disclosed, covers up to 1,100 payphones, about 1,000 from GEC Plessey Telecommunications, and 80 from Landys & Gyr AG of Switserland, over the next 12 months.