3rd party texting with Siri

iOS and iPadOS

Hi there,
About a year back, my friend had to get rid of his cell carrier due to expenses. He's been using iMessage to text to other iPhone users with no issues; until recently where it stopped working.
I think that he would need to reactivate his iMessaging service, but he can't do that without having SMS support; which would mean getting onto a cell plan again; which he can't afford right now.
Is there a 3rd party texting app that works well with voiceOver and Siri? I've done a bit of Googling, but haven't come up with much.