All VoIP numbers fall under 10DLC, which is the replacement for Short Codes, because they use APIs and other automated methods for sending and receiving the messages. There is no 1:1 relationship with a VoIP numbers as there is with a Mobile number.
Mobile numbers are categorized as Person-to-Person (P2P) meaning that a person with a personal device is sending a text to another person (ie mobile number to mobile number). VoIP numbers are categorized as Application-to-Person (A2P) which means an API or other application is used to send or receive texts as well as no 1:1 relationship. That means I could have a single VoIP number but 10 instances of Textable on 10 different phones all sending as the same number.
VoIP Providers can register as a P2P provider, Google Voice is one, meaning that it is meant for personal use and personal use only. It also means you can only use the provider’s interfaces which cannot allow for any mass texting or even 3rd party integration (ie. apps like Textable).
Now yes you could get a SIM card and do some hacking and setup a method to mass send texts, however, if A2P traffic is found going over P2P or Mobile:Mobile peers you will be fined by the FCC for it (like upwards of $10K). So please feel free to FAFO with this and see what happens.
Here’s the base issue with this, Twilio is not a residential/consumer carrier. Sure they will be more than happy to provide you services but you are not their market space. They have no desire to cater to residential users. The texting services provided by Twilio are 100% A2P/10DLC and thus are subject to those rules. The best you could do is become a Sole Proprietor which has some limitations but Twilio supports Sole Proprietor Brands/Campaigns.
This goes the same for a lot of the providers out there like Flowroute, Telnyx, etc. they are not marketing to residential/consumers they are business level providers. Yes, you can sign up and use them for personal use but again, they do not cater to the dad at home that wants to send a text to his wife saying “Can you grab a six pack while out?”
What makes this even more a kick in the junk than STIR/SHAKEN for calls is that a text message can be more than SPAM, it can be more than a “Auto Warranty” phishing scheme. The bad actors can send malicious attachments or links containing malware or other bad things that can end up on the phone or computer (since there is Text-to-Email delivery). That little additional factor makes something like 10DLC even more needed.