It's possible to switch completely to another Telco for both calls and line rental here, and it's a near-impossible task trying to keep up with all the package offers as each one tries to outdo the others to get business:
"Free calls to The Outer Hebrides on Sundays!"
"Ah, but we offer free calls to Outer Mongolia every other Monday between 8 and 9 p.m. so long as there's a full moon....."
I do sometimes feel that I'm fighting a losing battle though trying to explain to people around here that no matter who they pay for their line rental it is still BT which owns and maintains the local loop, and that any physical line faults they report to "their" telco will just be forwarded to BT to deal with.