Key Takeaways
- MCP for SMS is an adapter protocol: a host talks tools, your server talks REST, the Android radio still sends.
- Not a first-party Cursor/Claude plugin from us. Not a second SMSC.
- Security baseline: env keys, HMAC inbound, allowlisted send, no OTP in transcripts.
- Concepts sibling is vocabulary; this page is the threat model.
- BYO Android and operator credit. We meter devices and volume (Free 300 lifetime; paid from $19/mo).
Summary
Security view of what is MCP for SMS: a local or remote tool host, not a safer SMS network. Concepts: what is MCP for SMS. Adapter: SMS MCP server overview. Spec: modelcontextprotocol.io. REST: Developer Center.
MCP does not move SMS off the SIM. It only decides whether a model is allowed to enqueue a job on a phone you still own.
What MCP is (and is not)
It is a way for an agent to call tools. It is not carrier credit, not OEM immunity, not a first-party plugin. REST remains the contract.
Context
Teams hear “MCP” and skip pairing, last-seen, and HMAC. Those still dominate incidents. Setup.
Security baseline
- Env API key; never mcp.json.
- Least-privilege: read tools on, open send off.
- HMAC-verify inbound before side effects.
- Redact bodies in logs and chat.
- OTP on the product path, not the agent path.
Layer table
| Layer | Does | Security job |
|---|---|---|
| Host (Cursor / Desktop) | Chooses tools | No secrets in chat |
| MCP server | Maps tools → HTTP | Allowlist, HMAC, env key |
| Gateway REST | Queues a device | Authn as documented |
| Android + SIM | Radio | Airtime, OEM, last-seen |
Tools still meter volume
Accepted sends hit devices + volume and the operator. Pricing.
Operations
OEM sleep is not an MCP outage. Keep a spare charged handset.
HMAC and least privilege
Verify signatures on the raw body. Webhooks. Keys: auth and API keys.
Decision guide
Use MCP for constrained ops. Use REST for customer OTP. If send is unbounded, do not enable the server.
Checklist
- No first-party plugin claim.
- Env key; HMAC inbound.
- Open send off.
- Bodies redacted.
- Phone last-seen alerted.
Next steps
Multi-tenant isolation: multi-tenant MCP considerations.
Related product pages
Jump to the live product docs for this topic—not another long-form article.
- SMS API documentationLive endpoint reference
- device and SMS volume pricingPlans and allowances
- Security and Trust CenterCompliance and posture
- Android SMS gateway product guideDefinition, product, and how to buy
