Exactly the same providers as anywhere else in the country.
Often the subtext when consumers claim ( inaccurately ) that they are limited to using BT , is that BT are somehow limiting their choice , this is nonsense of course, there is a world of difference between providers with exactly the same access to the supplier that BT use ( Openreach ) to offer service, or a combination of services but deciding not to offer a directly comparable set of services ( for their own reasons ) , and being denied the opportunity to do so .
So , if you require a ‘landline’ telephone service but can’t find a supplier other than BT , that’s because whoever it is you want to use have decided it’s not in their financial interest to offer it , however , you can get a comparable phone service from Sky , Now , Talk Talk and Vodafone ( to name just four , it’s not an exhaustive list ) , as stated , there isn’t a single area , anywhere in the entire UK that only has a choice of BT , it’s just not true , so your area of West Cumbria, even if it’s the remotest place imaginable has a choice, if the choice isn’t are extensive as you would like , blame the companies that have chosen to ignore that area rather than the ones that have decided to provide a service there.
There are multiple providers that can utilise the Openreach infrastructure.
Have you also checked for Alternative network providers in your area? You can use https://labs.thinkbroadband.com/local/postcode-search or https://checker.ofcom.org.uk/en-gb/broadband-coverage to help check what network providers are available.
Even if Openreach infrastructure is only available and other providers may only offer a broadband only service there is also the option where you can also move to a third party Voice over IP provider to allow you to have a home phone service.
Phone numbers maybe ported to another service after cancellation if the request is made within the 30 days of the previous phone service being cancelled (in some cases such as home moves, phone numbers may not be able to be ported)
https://www.ofcom.org.uk/phones-and-broadband/switching-provider/switching-landline/