"We get a lot of spam from those" would fall well within a vaguely defined "valid reason", I'd think.
(Most of my SMS spam comes from .info domains.)
>Most of my SMS spam comes from .info domains
Do you mean that the SMS messages contain links to .info domains?
Yes.
I've personally noticed a lot of phone text spam being FROM email addresses recently. I think they are just abusing some feature in MMS, though, not SMS. It's weird seeing a list of phone numbers (usually SMS two-factor), some contacts' names that I have entered in, then a ton of random email addresses on my texting app (standard Android Messages app).