zlacker

>>mikece+(OP)
$6 million per year on outgoing SMS? Do not send SMS to users, make users send SMS to you instead to confirm their numbers! I have this solution for years and it works >90% of the time. The rest 10% is calling a verification number which drops calls with busy signal (no fees for the caller) but sees who is calling and is able to verify their number.

>>vizzah+PV
Significantly less secure. Faking the sending number is much easier than hacking SS7 and getting SMS routed to you which are not destined to you (which is also doable but require an order of magnitude more skills and ressources in my view).

>>illiac+pY
This is correct; anyone with relatively basic knowledge of VOIP can spoof any number (and CID name) they want.