Send SMS with a GSM modem Part 1 - MultiTech MultiModem setup - YouTube
Create your own SMS Server/Gateway - Robert Andresen
GitHub - nerdinand/SMSGateway: A very hacky Android SMS gateway app. Enables you to connect via telnet via USB (after forwarding a port with adb) and send and receive SMS via the phone.
4G LTE 8 Port GSM Modem For Bulk SMS With HTTP API Support Text Message Broadcasting Device From Senlink, $440.13 | DHgate.Com