Solving this is squarely Twilio's business!
They know how much to bill the customer, so they must know how much it costs to send to a number.
They know how much to bill the customer, so they must know how much it costs to send to a number.
I don't mean to do Twilio's work of defending them, but in my experience it's possible they actually don't know how much to bill the customer. What they may know is the generalized per-minute or per-session rate they've agreed with another operator alongside a general "premium rate numbers will be settled at a later date" kind of clause.
My employer got bit by this several years ago, purely on calls within the +1 country code. Before this practice was largely banned, some small carriers were allowed to designate certain rate centers as higher cost. So our VoIP carrier would say that a call to a given area code was $0.003/minute but the calls would later settle out at $0.25/minute because of a 1,000s block of numbers being (unknowing to us our our carrier) as higher cost and being settlement billed back at the higher rate.
Twilio could agree to carry some or all of this risk for its customers as part of their value-add and fees. That way, Twilio has the incentive to make the proper changes for its customers and would have the experience of looking at all of the return billed rates for all of the calls or messages across its entire customer base to help prevent toll fraud.
There have been people who got printed bills from their cell phone provider for every single kilobyte of data, each individually indexed and billed: https://en.wikipedia.org/wiki/300-page_iPhone_bill
Really sucks when you carefully load 10 EUR of credit to buy a 10 EUR prepaid plan for the month and see 0,05 deducted despite being incredibly careful to not do anything that would incur a charge before buying the plan.
There is a pop up that says "Your carrier may charge for the messages used to activate iMessage and Facetime" You can choose to not activate and do it later.
There’s a field in there that configured whether that warning should be shown.
My memory, which may be wrong, is telling me that the first major version of iOS which included iMessage did not include the warning at all, and that it was added for non-whitelisted carriers (aka those which did not sell the iPhone) to prepare the user for the possibility that they will be billed, based on user feedback precisely like the comment to which I was replying.
The company had made a change of some sort where whatever EDI connection between the telco and the company stopped working. I learned this when and angry facilities guy came up looking for my boss’s boss to sign for a delivery. I was the only person there, so I did. 15 minutes later, two pallets of bankers boxes came up - thousands of single sided pages of itemized call details.
(FreeConferenceCall and similar companies lobbied heavily against this rule, but AT&T and Verizon were able to lobby it through.)
Ugh.
If Twilio cops an unexpectedly high settlement for sending an SMS to +1234567890 in January, can they assume that a separate customer sending an SMS to that number in February will end up in the same boat?
I'd be very surprised if the toll fraudsters weren't using the same numbers to hit multiple Twilio accounts.