If I remember correctly standard SMS has no security on it at all and is in the clear during transit. I may be wrong and never scared of being corrected.
Assume anything sent over a cellular network carrier via normal SMS can not only be retrieved, but intercepted.
Thank goodness a lot of companies regularly use it for 2FA.
Telecommunication is highly regulated. They have to keep records for a long time and make them available to law enforcement.
IIUC, they can get 7 years worth of SMS/MMS (including contents) with very little effort/cost.
They've been inside the phone companies for a long time so I assume they have full access to SMS.