I think in the short term its cheaper for these scam call centres to use "local" English speakers (in practice many of the employees are fresh-faced out-of-towners looking for their first job) than it is to dev and maintain an entire GPT pipeline. It will require a level of completely different organisation and sophistication than what is currently in place. Right now outside of running the dialler and internal off-the-shelf packages to manage their workforce these orgs are not particularly tech literate as evidenced by the YouTube channels that expose them.