The trio planned a series of up to eight explosions at unknown targets across the UK between December 25, 2010, and September 19 last year, it is alleged.
Each timer-triggered device is said to have been capable of killing up to 25 people and injuring scores more.
Naseer, of Doris Road, Sparkhill, Birmingham, denies five counts of engaging in conduct in preparation of terrorist acts.
Khalid, of Timbers Way, Sparkbrook, Birmingham, denies four counts of engaging in conduct in preparation of terrorist acts.
Ali, of White Street, Birmingham, denies three counts of engaging in conduct in preparation of terrorist acts.
