What's stopping robo call companies from using regular sim cards once all voip providers close their doors.
You can buy jigs on aliexpress that hold 128 SIMs and round-Robin across 8 GSM radios.
It’s not all for spam per se. Some countries/providers charge a ton for international incoming calls, so bypassing this by IP and making calls in-provider only saves a lot of $$$ for gray-market connectivity.
And it’s cheaper for setting up of in-bound calls too than a business line.
https://m.aliexpress.com/item/32947688074.html?spm=a2g0n.pro...
Or 32 SIMs with 32 radios:
https://m.aliexpress.com/item/32819345650.html?spm=a2g0n.det...
Most of these guys will charge you 10-20% less than bandwidth.com or Twilio will in return for slightly lower reliability. nCLI means you can't set caller ID because the call is coming over GSM, i.e. a simbox type setup. TDM usually means they are reselling traditional phone lines meant for businesses. If you think this already isn't being used to facilitate scams you'd be wrong: https://globalvoipforum.com/threads/offering-russia-for-fore... (unless by "forex traffic" they mean promoting Interactive Brokers). That's an example I found in 5 seconds. Go on some Facebook groups and you will find people offering grey routes to call America for "Amazon traffic," "bank traffic," "crypto traffic." I never really took the time to investigate what those terms mean but it does not sound good to me.