Some AT&T customers went to their mailboxes last week to discover a surprise from the phone company: A free smartphone.

The upgrade was offered to a handful of AT&T customers who are still using devices on the wireless company’s older, 3G wireless network — one that is expected to be shut down by the end of this year.

In June, AT&T said it would offer free smartphones to customers who were still relying on the old network and whose current devices were not compatible with the company’s newer 4G/LTE and 5G networks.

At the time, AT&T said the free upgrade would be in the form of a new AT&T Radiant Core, an $80 smartphone that is capable of making voice-over-LTE (VoLTE) calls on the company’s network.

But some customers last week reported receiving better devices than the basic smartphone that was once promised: In online forums, AT&T postpaid customers said packages delivered by AT&T contained Samsung Galaxy phones that typically fetch a higher price than the Radiant Core.

Those devices include the Samsung Galaxy S9, the Galaxy Note 9, the Galaxy Note 10 and the Galaxy A11.

A spokesperson for AT&T confirmed some customers would receive newer and nicer devices than the AT&T Radiant Core due to supply constraints, suggesting a large number of the company’s wireless customers are still relying on non-compatible devices.

“We have not changed our plans to replace 3G network-dependent devices,” the spokesperson said. “However, inventory constraints mean we sometimes must find substitutes for some devices.”

AT&T says customers who receive new devices must activate them on their current AT&T plan within 30 days of receiving them, and that their older devices will stop working once the new one is activated.