For the isles this means the end of frustration of failing phone lines caused by the microwave link dropping out when it is replaced by a cable connection in December.
BT is also offering businesses and public agencies a new Ethernet service in Lerwick to purchase broadband speeds of up to 10 gigabits per second, vastly more than anyone currently requires.
For the rest of Shetland’s broadband users they can expect nothing faster than they currently receive, unless they live in Lerwick, where BT is promising speeds of up to 20 megabits per second.
Meanwhile BT is addressing harsh criticism of its complaints system, by setting up a network of local “spotters” who will be able to report faults from areas around the isles.
Currently islanders complain that they are regularly fobbed off when they call BT to tell them their internet is not working.
To achieve more reliable broadband and phone lines, BT is finally using - “lighting up” - the capacity it already leases on the Faroese SHEFA 2 fibre optic cable that came ashore on Shetland six years ago.
It will also now lease space on the £1 million council-funded Shetland Telecom fibre optic cable that connects SHEFA 2 with Lerwick and Scalloway.
Shetland Telecom project manager Marvin Smith said he was delighted with Monday’s unexpected news.
“This is a monumental day. It’s been 10 years since we started trying to get BT to provide a fibre optic link to Shetland,” he said.
“This will get rid of Shetland’s dependence on the microwave link, so BT customers will now have a reliable connection with the rest of the world.”
Weather conditions regularly play havoc with Shetland’s communications network as the microwave link can be interrupted by atmospheric disturbance.
“Broadband customers will no longer lose their connection because of bad weather, good weather, atmospherics, all things that grind Shetland to a halt,” Smith said.
While the investment will not improve broadband speeds outside of Lerwick where some people could attain speeds of up to 16 megabits per second, Smith said it could prove to be “a stepping stone” to providing faster connections in the future.
Speaking at the Northern Isles Digital Forum, at Islesburgh community centre, on Monday, BT Scotland director Brendan Dick said: “By investing £8 million in this fibre spine for Orkney, Shetland and the north of Scotland, BT is laying the building blocks for any future deployment of fibre broadband.”
Shetland MSP Tavish Scott, who chaired the forum, welcomed Dick's announcement, but said there was still a long way to go down the digital route in the isles.
“There is still much to do because many areas of Shetland have next to no broadband," he said.
"Many local people still feel that the broadband service they pay for does not meet the advertised standards.
“This can be for any provider of broadband services such as Sky, Talk Talk or BT Retail.
“People should get what they pay for and if they don't they should either pay less or receive compensation.
“I will be pursuing this with the telecoms regulator and Alistair Carmichael as the improvements announced today will not benefit all islanders."