The two firms will work alongside smaller practices chosen to represent five regions as the £500m-a-year client attempts to whittle down its supplier base to increase efficiency.
BT senior manager for the construction supply chain, Paul Carlaw, said two national firms had been chosen to complement the regional architects because of their ability to handle larger projects.
He said: "It was felt that, for the more complex buildings, the national architects would be able to build up a better understanding than the regional firms.
"They might have better CAD facilities and produce better video imaging and visual walk-through aids to help staff prepare for changes," he said.
Each of the regions, except London and the Home Counties, will be allocated an architect. Two or three practices will be picked for the London region.
These firms will carry out projects worth £2m or less, with the national firms taking over on bigger projects.
Industry sources said the position on the framework list was likely to mean a workload bonanza for BDP and Aukett – BT has spent up to £200m on major projects in recent years. In addition to call centres and offices, the two practices will be asked to design projects worth as little as £500 000 if BT decides these have "prestige" status.
Carlaw added that regional architects may also find themselves competing with building surveyors for design work on projects worth £150 000 or less.
BT is also on the verge of selecting framework building surveyors, but it has already picked a series of M&E consultants to work for it on a regional basis.
Capita Property Services has been selected in the Home Counties, Kennedy & Donkin will cover Wales, the Midlands and the West; WS Atkins has been chosen for the North; and Wallace Whittle will operate in Scotland.
Firms are selected on the basis of an in-depth scrutiny of their price, personnel, qualifications, quality assurance and track record.
In the long term, BT is also planning to alter the way it selects contractors, with new procurement proposals due to go to its board soon.
Firms have been invited to bid for inclusion on the list, which will see the winners awarded a steady stream of small, mainly retail assignments.