I kept my UK landline number by porting it to VoIP when I switched to fibre. The basics: open an account, submit a Letter of Authority and a recent bill, pick a port date. Mine took 7 days. Hardware-wise I used a Grandstream HT801 so my old cordless base plugged in like normal, plus a cheap UPS to keep the router/ATA alive for brief outages. Costs were a one-off porting fee, a couple quid a month for the number, and pay-as-you-go calls. Call quality’s been solid. I did the port with
telxi and the self-serve setup was painless. It works with 3CX and Zoiper, pricing is pay-as-you-use, and support replied fast at odd hours.