Some 3,340 calls made in Scotland were diverted to England between January to July , the most recent figures suggest.
Meanwhile, 974 calls made in England were diverted to Scottish control rooms in the same period.
Figures released under the Freedom of Information Act show the vast majority of calls were diverted in January, after an outbreak of Covid-19 at the Glasgow control room in Cardonald.
English control rooms took 2,245 calls from Scotland in that month, while the SAS took 171 from England.
The figures also showed staff absences due to Covid-19 in the SAS more than doubled from May to July this year, with 154 recorded in May, 314 in June, and 340 in July.
Of these, there were 135 Covid-related absences among frontline paramedics and technicians in May, compared to 309 in July. There were 19 control room staff absent in May, and 31 in June.
These figures relate to staff absent with illness from Covid-19, or due to self-isolation.
The SAS has a long-standing agreement with other services in England, Wales and Northern Ireland to support each other during times of high pressure.
The process is managed by phone provider BT, which automatically re-routes calls when needed so as to limit delays in answering.
The SAS said there is no delay in responding to calls when this happens, as the information taken by one service will be digitally transferred back to the other.
A spokesperson for the service said: "The long-standing mutual aid arrangements, which are in place between Scotland, England, Northern Ireland and Wales, help ease pressures at various times across the four nations.
"As was publicised at the time, in January a small number of our staff in the west of Scotland were isolating after testing positive for Covid-19 and other members of staff self-isolated due to test and protect measures. This led to a small percentage of calls being diverted to other areas.
"The Scottish Ambulance Service have also supported other ambulance services when they have experienced pressures and we appreciate their assistance."
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