There is a difference between a number managed by a traditional carrier using VOIP and a number from a free/low cost VOIP provider, especially when you are using text verification as a anti-spam measure.
>We find that miscreants rampantly abuse free VOIP services to circumvent the intended cost of acquiring phone numbers, in effect undermining phone verification. Combined with short lived phone numbers from India and Indonesia that we suspect are tied to human verification farms, this confluence of factors correlates with a market-wide price drop of 30-40% for Google PVA until Google penalized verification from frequently abused carriers
>We find that miscreants rampantly abuse free VOIP services to circumvent the intended cost of acquiring phone numbers, in effect undermining phone verification. Combined with short lived phone numbers from India and Indonesia that we suspect are tied to human verification farms, this confluence of factors correlates with a market-wide price drop of 30-40% for Google PVA until Google penalized verification from frequently abused carriers
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