sorry, no idea how i missed that in the first sentence of your post
in that case, i'd
divert that mobile number to a VoIP phone number, which would not only allow receiving (and making) calls via the VoIP provider's app,
but also do the same with sms
on second thoughts, think that you'd actually need to transfer/port your mobile number to the VoIP provider to receive/send sms via their app
as you have an iPhone, perhaps the sms forwarding to other Apple devices feature might work?
With the Text Message Forwarding feature of your iPhone, the SMS, MMS or RCS messages that you send and receive on your iPhone can also appear on your Mac, iPad and Apple Vision Pro.
support.apple.com