Something like Require-Recipient-Valid-Since from SMTP? That would be neat. Does SMS have the necessary protocol flexibility to allow that to be added?
The User Data Header of SMS [0] isn't very flexible, and quite constrained - both it and the message needs to fit inside a 140 byte payload.
There are a handful of bytes reserved for a future purpose, which could be used for something like this, but you're limiting how large the message can be, likely significantly.
