this new carrier does not support iMessage
This Carrier (C) chooses to not support iMessage.
That's their prerogative.
I do not really know what your native language actually is (Dutch? Afrikaans? Spanish? English? Swahili?); but I know that--no matter the medium--we can always achieve some degree of mutually-satisfying communication. Through conversion, and translation.
If an individual finds themselves communicating entirely with those of their familial, natal, natural, societal-hapolal-clade, inter-personal communication revolves to a simplistic, mono-bloc(ian) pattern.
*record-scratch*
*cough*
I'm currently in the process of achieving State-Standards-Certification for Teaching, and--at this time--I am (attempting to visualize the concept of the replication of DNA) 🤷♂️
So, let me leave this with you:
"Find a Carrier that supports what you want to do."