Think the OP has a BT Retail line but yes BT Openreach have to fix it (for no charge) as the line is already provided. You don't get much (aka any) say in how the service is provided, if BT decided it was cheaper for them to put in FTTP and conversion kit to POTS that is what they would do. Asking for a certain pole or chamber will require your to pay for any extra works...
Once a line has been provided BT Openreach are contractually obliged to fix it within the terms of the contract and your service level. If that fix requires them to open up two miles of trench, relay ducts, pull in new cable then that is what they will do and no charge to you. They might not make the within four working days for a residential line target if they had to do that though. B-)
Worth a few tests like that just to ensure that the crackles are within the BT network, if they come out and the fault is with your wiring or equipment there is a £99 charge...
Just done that myself, ported a couple of BT numbers to Sipgate. Works well with a Gigaset N300 PSTN/VoIP/DECT unit. As we have no choice of telecoms provider I've also added "Total Care" to the residential POTS line that brings in the ADSL. Total Care means that they aim to fix faults within 24 hrs of the report (fix is within working hours, something like 0800 to 1800 365 days/year). Worked last week about 10 days after applying Total Care, reported fault just before 1700 Thursday, fixed about 1100 Friday. B-) A side effect of Total Care seems to be that you can't report faults online, you have to speak to Bangalore. Total Care on a residential line costs £4.00/month.
Sipgate are free in that there is no regular monthly fee for the service, calls are still chargeable... But considerably less than BT, the *minimum* charge for a daytime call landline to landline via BT is 23p.
I considered that but decided that I'd rather support Sipgate properly by using them for calls. Their web interface, options and voicemail (notification by (chargeable) SMS, email with/without the recording attached) on the "free" service is very good.
You can access voicemail via the web as well and I think set (chargeable) diverts but you need internet access to do that. So if your net connection is down... Of course you could use a smartphone just to set the diverts.
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