The upgrades and building will provide residents, businesses and visitors in rural communities with faster and more reliable mobile coverage.
While these 100 sites are controlled by Virgin Media O2, whose customers can now receive reliable 4G services at 146 rural locations, customers of Three and Vodafone will also benefit from the rollout.
The Isle of Skye, Scotland’s second-largest island, became the 100th site to where improved mobile connectivity has been provided after Virgin Media O2 used helicopters to deliver and install new 4G masts there.
The SRN is a £1 billion joint initiative between MNOs and government to extend 4G connectivity to 95 per cent of the UK’s landmass by the end of 2025.
Of the 100 rural sites, 78 are in some of the most remote parts of Scotland, including Shetland, Ardross, and Argyll & Bute, while 19 are in rural parts of England, including parts of Yorkshire, Suffolk and Kent, and three are in Northern Ireland.
The upgrades provide customers with faster and more reliable mobile data, and higher quality voice calls.
Jeanie York, chief technology officer at Virgin Media O2, said, "We’re going to extreme lengths connecting the most remote corners of the UK to deliver our share of the Shared Rural Network.
"This investment is vital to ensure we provide fast and reliable coverage to all areas of the UK. With so much of our modern life taking place online, rural communities deserve the same standard of mobile connectivity as those in urban areas, and we’re proud to be stepping up and playing our part.
"The 100 sites we have delivered will mean that more residents, businesses and visitors in rural areas can benefit from better mobile coverage, with more locations to follow in the coming months. This work is vital in tackling the urban-rural digital divide that exists in the UK."