We've been doing this for a few years now, ever since
NGT[1] made it possible to use an internet client for textphone calls rather than a retro 1970-technology Minicom on a BT
[2] analogue line.
We're not big voice telephony users. I pretty much only use it to deal with luddite bureaucratic organisations like banks, government departments and the NHS who can't cope with more civilised forms of communication. Barakta uses it with an amplified phone to talk to her mum and a couple of patient friends who struggle to access text for disability reasons.
As a side effect of general mucking about with Asterisk, it became readily apparent that the signal:noise ratio was much better on SIP (using the G.711 codecs to Sipgate) than it was on the BT analogue line, which makes all the difference in terms of barakta being able to hear (we both struggle to hear if there's any GSM involved, which rules out mobile phones). When we no longer needed POTS for the Minicom, we got AAISP to take over the line as a broadband-only
[3] service. And just like that, the spam calls stopped.
Sipgate isn't landline-levels of reliable, but that's fine for our purposes. PAYG suits our low level of useage.
So yeah, VOIP can work well, but my general advice would be:
- Use proper standards-based VOIP, not proprietary solutions like Skype.
- Use dedicated hardware phones if possible. Soft phones on the desktop are faff to answer (hearing people only give you a few seconds to answer a phone these days), and smartphone implementations are dubious bordering on broken. You can get Snom 300s for under 20 quid on eBay.
- I've never met an ATA that I actually liked.
- You need a decent internet connection. WiFi is best avoided, and it works much better if you either have traffic shaping at each end to prioritise the VOIP packets, or enough bandwidth that the link never becomes congested.
[1] Or whatever they've re-branded as this 5 minutes.
[2] And it pretty much had to be BT, otherwise you couldn't use the 1800X prefixes to route the call through relay.
[3] It provides VDSL in the usual way. If you plug a telephone into the line you get a recorded message telling the engineer what line it is and not to steal the pair. We pay about a quid less per month for this than we would for a voice-calls provider, because that's how Openreach charge for the infrastructure.