I had over 2 years of VoIP service with free calls to the UK, USA, Canada, Aus, NZ and a few other countries, all for the grand sum of £6. That's £6 for 2 years.
I just paid a few quid on top of that for my ATA.
No phone line rental, used my cable broadband.
The only reason about 6 weeks ago I had a cable phone line put in was it was installed for free, I don't pay line rental, I get evening and weekend package free and caller display for free. VM didn't want to lose me as a customer, played them at their own game, so they gave me the phone service free and discounted my package.
So now I use VM for the free calls with them and VoIP for the calls not free on VM.
Not had any reliability problem with my VoIP service.