This is a logical offer for them to make. Many of their customers will have unlocked phones, so they aren't in a position to force those customers to use overpr

This is a logical offer for them to make. Many of their customers will have unlocked phones, so they aren't in a position to force those customers to use overpriced international data plans (e.g. AT&T's $120 for 800MB/mo). The competition is the cheap nano-SIM card in the airport vending machine.