I keep receiving sms messages from short code number with the following text:
Configuration Notification. Your MMS Service Settings have arrived. Open the configuration message and save the settings.
the messages never contain settings or an attachment which I would not have trusted anyways
I have received them from the following short codes: 909, 5129, 5126, 5128, 5127. I'm using a one plus 3t and I have verified I am using the correct messaging settings as per https://support.t-mobile.com/docs/DOC-2090
Best answer by tmo_amandaView original