They do have automated filtering by IMEI for smartphone / dumbphone -- every handset line has a specific IMEI sequence and they update the filter when new phone

They do have automated filtering by IMEI for smartphone / dumbphone -- every handset line has a specific IMEI sequence and they update the filter when new phones are released fir AT&T. Your guess is as good as mine on how up to date those filters are for not-released-on-ATT phones.