Founder & CEO of Plivo - https://www.plivo.com/ here. At Plivo we offer similar API services to Twilio for voice calls and SMS. While API offerings have made it easier for developers and tech team to integrate communications into their applications, one of the challenges here is the scale at which spammers and folks using stolen credit cards are always attempting to abuse all of our platforms.
Most of us companies, work quite hard to deter these spammers at sign up and later using automated systems to analyze usage patterns including content filtering, but its quite a cat and mouse game.
Something that has worked for us has been to restrict signups to only work emails. It does have it's disadvantages but we have been able to limit the random gmail id signups at scale by bot/spammers that abuse the system for use cases like robocalling and more.
Plivo's API above is updated on a daily basis for portability information.
Caller ID as you mention for voice calls is quite easy to spoof, however with the STIR SHAKEN rollout, the intention is to make carriers accountable. SMS however with 10DLC is almost impossible to spoof the number.