The call was made from a phone box in East Kilbride at 0945 last Wednesday morning.
The Group 4 driver was tied up and locked in the back of the van by three robbers who escaped with at least £100,000.
He was released after spending four hours in the vehicle at Falls of Falloch, five miles south of Crianlarich on the A82.
The new information about the raid has been released by police who renewed their appeal for help.
Detective Chief Inspector Andy Price said "considerable progress" had been made since the investigation began.
Inquiries continued to be made in the Lairhills Road and Livingstone Drive area of East Kilbride where the public phone box is located.
He also asked for a lorry driver who was going north on the A82 near Ardlui, near the robbery scene, betwen 0600 and 0645 BST last Wednesday, to come forward.#
DCI Price said the driver may have information which could be of "significant assistance".
The 29-year-old security van driver was "badly shaken" by the incident but was otherwise unhurt.
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