Zadarma, looks like it might be good. No direct KYC and seems a little lax.
Hard to find these days since most providers need verification. You could try smaller or self-hosted options like Gammu, Kannel, or use a GSM modem with a prepaid SIM to skip KYC.
These open source options look cool however the main issue combatting bulk calls/sms is not KYC directly but the "shaken/stir" laws in the US. If you were doing things on your own you'd still need to apply for an Operating Company Number (OCN) with the National Exchange Carrier Association and register with the FCC and their Robotcall Mitigation Database. It's not as easy as simply using open source (unfortunately).
