Teli has treated us well for years, they use some small cell provider in the midwest for SMS/MMS enablement. Signalwire is essentially Bandwidth.com without the sales funnel.
FWIW, I looked through the APIs and while I did see mechanisms for rejecting phone calls and faxes, I did not see a way to block specific numbers from sending you SMS. Not that it matters, free inbound more or less solves the problem. Thanks again.