Best answer by Mohammed
The 20GB plans are for SIM-only contracts only.
The maximum available for the iPhone SE 128GB is 8GB.
This is for a handset contract so the deals work a little differently.
It'll still have data rollover, so any unused data from that 8GB will rollover to the next month up to 30-days at a time.
It's not possible to get the 20GB plan on an iPhone 8 contract.