We verified AT&T and Cricket SIM card.
This does not relate to IMEI. They take whatever IMEI.
The problem is the apn, as @sfx2000 said.
AT&T may use the apn “phone”
Cricket may use the apn “ndo”
After applying the correct apn, SIM card just connects.
Furthermore, if you have more issues, pls try the 2 AT commands below to get the SIM card info an apn settings. Then search the carrier’s website to verify if the apn is correct or not. If not, find the correct apn and set up.
AT+CIMI
AT+CGDCONT?