sentences:  The prototype for the exchange which the GPO called TXE2 was a system called Pentex (the Plessey trademark for all non-GPO sales), which, starting in 1963, was developed by Ericsson Telephones, as part of Plessey.The first field trial of Pentex started in the Peterborough Telephone Area in 1965.There was another trial site at Leamington.