I switched from Verizon to T-mobile yesterday, and the salesman sold me a Samsung Galaxy S10e with 256GB for the same price as the 128MB model. The T-mobile store price is $749.
He said it was an unpublished promotion that anyone could purchase. I didn't ask how long the promotion would last. It also looks like you have to go to a store to get the promotion because the T-mobile website doesn't even list the 256 GB model and the Samsung website only shows the 256GB model available at Samsung stores.