I think the AT&T sensors are actually non-zwave, or they may be using the z-wave protocol on a modified frequency: 433MHz. They are definitely not in the 900MHz spectrum… so you won’t be able to pair them to ST directly. I use them with AT&T and have an integration that brings them all into ST, but they’re not directly connected to ST.
I also think some work on the 915Mhz, if you have a signal booster, look at its part number. SW-ATT-RPTR4 works on 433MHz, SW-ATT-RPTR9 works on 915MHz.