If you don't absolutely need this to originate from a mobile subscription with your name on it, you can for far less money get a DID ("direct inwards dial"; the term colloquially means a virtual mobile number) with any of the numerous VoIP providers out there. Most of them not only provide in- and outbound calls on those DIDs, but also ditto for SMSes. The interface for voice calls is almost exclusively SIP, and for SMSes it's usually an HTTP-based API.

If you go this route, make sure you absolutely know how to, and that you absolutely lock this down. SIP toll fraud is still a problem and if it happens to you, it can get destructively expensive.

https://www.twilio.com/learn/voice-and-video/toll-fraud

Common sense obviously applies. With a cell phone, don't call back to unknown numbers ringing once or twice ("wangiri"). With a SIP trunk, don't allow remote anonymous access.

Yeah I suppose it's really easy to call this common-sense, it probably should be common-sense.

Yet at the same time, if it were common-sense in practice, I probably wouldn't have a job.

These services are great, except for the sites with mandatory sms 2fa that refuse to send to voip phone numbers (I'm looking at you, Apple).

If you use XMPP checkout https://jmp.chat/ .

This is pretty interesting, I'm going to give it a go setting something like this up with ejabberd and their asterisk fork, that way I can use my own sim cards.