Summary of callcentric:
- perfect web interface for shoppers, evaluators, and paying customers (more below).
- perfectly upfront with prices for shoppers -- zero surprises once you are paying customer.
- 911 USA service fee ($1.50/month elsewhere) is included in "make call" plans.
- the most extensive FAQ of any VoIP I've shopped by far. You will be fully informed.
- sound quality is fine.
- excellent (fast, knowledgeable) customer support: got help with
configuring ATA, verifying a caller ID number, and porting my legacy telephone number.
- (june 2019) porting my legacy number was free. $15 elsewhere.

Details:
I'm a callcentric paying customer since June 2019, "north america basic"
and "pay per minute" plans. Formerly a lingo customer since 2007;
formerly a sunrocket customer since circa 2006.

Callcentric is a BYOD* (bring your own device) VoIP service unlike lingo
was. The linksys 2102-R from the former service lingo seemed (to me)
to be hopelessly locked to them. So I bought a Grandstream HT801 analog
telephone adapter (ATA) for $27.10 from amazon as it was the cheapest of
what seemed to me to be mainstream ATAs. And callcentric recommended it.
Actually, they recommended the HT802, but seems the HT801 is the same with
only one telephone port which is all I need. This Grandstream device
is working fine despite the firmware version being one release old.

When configuring my grandstream ht801 I made a typo. Symptom was test
phone call failed. Callcentric customer service correctly theorized
my mistake and got me sorted straight away, and also told me this which
is not (june 2019) in the online instructions for when configuring the HT80x:

Please also make the following changes:
Use P-Access-Network-Info Header: No
Use P-Emergency-Info Header: No

About my typo: look carefully because the grandstream configuration
has fields "dial plan prefix" and "dial plan." You will be configuring
the later.

* To non-experts: I really do think you can configure the ATA device
correctly. Don't be intimidated. Yes, in my case I should have looked
more carefully at field names, but even when I did make a configuration
mistake, callcentric support got me going on the first reply to my email
plea for assistance.

About the callcentric.com website. It is perfect. The layout is
correctly targeted for a real computer (desktop) not a littlescreen
cell phone. The fonts are similar enough sized so you can read the
whole page easily at once. No dumb animations, fades or fluff; very fast
and responsive. No useless whitespace; no ridiculous need to widen
the browser to see all of the page. No annoying popup sales offers or
"chat with us" dialog boxes. No popup banner thrust in your face when
logging in. The password requirement isn't onerous. No dopey image
of some smiling human using a telephone to distract and slow down load
& render times. Website login does not timeout too quickly, but I
don't know what the timeout value is and I can't find where to adjust
it anyway. Time/dates shown are per my local timezone -- seems obvious
but in lingo's reports the time/dates were in GMT...sheesh! Layout & tabs
are well organized. Seems my bank (and google) changes website layouts
periodically and it is often for the worse IMHO. I *still* hate gmail's
new UI. I hope callcentric never changes their web site or reports.

My first full month bill came in exactly as I expected when buying
the service. No surprises. Actual July 2019 bill was $7.23. This is
$1.95 inbound calling plan, $1.95 outbound plan, $0 taxes/fees, $3.33
in per minute charges at 1.5cents/min inbound, and 2c/min outbound to
USA when exceeding the included 120min/month.

About the spam call filter feature, this seems promising. I just don't
yet have examples of telemarketers who were successfully blocked, going
by the online call reports. The website interface for this feature
looks great. I played with it, and I setup to have all incoming calls
that are flagged as spam probability "high" get the "press 4 to continue"
interceding challenge message before ringing through to my telephone
adapter. Note: callcentric is upfront in saying this feature will cost
you 1.5 cents (pay per minute plan) because the call does need to be
connected to play the challenge message.